<?php
/**
* SeekQuarry/Yioop --
* Open Source Pure PHP Search Engine, Crawler, and Indexer
*
* Copyright (C) 2009 - 2014 Chris Pollett chris@pollett.org
*
* LICENSE:
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* END LICENSE
*
* @author Chris Pollett chris@pollett.org
* @package seek_quarry
* @subpackage library
* @license http://www.gnu.org/licenses/ GPL3
* @link http://www.seekquarry.com/
* @copyright 2009 - 2014
* @filesource
*/
if(!defined('BASE_DIR')) {echo "BAD REQUEST"; exit();}
/**
* Read in base class, if necessary
*/
require_once "persistent_structure.php";
/**
* Load charCopy
*/
require_once "utility.php";
/**
*Loads common constants for web crawling
*/
require_once BASE_DIR.'/lib/crawl_constants.php';
/** For CrawlDaemon::processHandler function */
require_once BASE_DIR."/lib/crawl_daemon.php";
/**
* Data structure used to store one generation worth of the word document
* index (inverted index).
* This data structure consists of three main components a word entries,
* word_doc entries, and document entries.
*
* Word entries are described in the documentation for the words field.
*
* Word-doc entries are described in the documentation for the word_docs field
*
* Document entries are described in the documentation for the doc_infos field
*
* IndexShards also have two access modes a $read_only_from_disk mode and
* a loaded in memory mode. Loaded in memory mode is mainly for writing new
* data to the shard. When in memory, data in the shard can also be in one of
* two states packed or unpacked. Roughly, when it is in a packed state it is
* ready to be serialized to disk; when it is an unpacked state it methods
* for adding data can be used.
*
* Serialized on disk, a shard has a header with document statistics followed
* by the a prefix index into the words component, followed by the word
* component itself, then the word-docs component, and finally the document
* component.
*
* @author Chris Pollett
*
* @package seek_quarry
* @subpackage library
*/
class IndexShard extends PersistentStructure implements
CrawlConstants
{
/**
* Stores document id's and links to documents id's together with
* summary offset information, and number of words in the doc/link
* The format for a record is 4 byte offset, followed by
* 3 bytes for the document length, followed by 1 byte containing
* the number of 8 byte doc key strings that make up the doc id (2 for
* a doc, 3 for a link), followed by the doc key strings themselves.
* In the case of a document the first doc key string has a hash of the
* url, the second a hash a tag stripped version of the document.
* In the case of a link, the keys are a unique identifier for the link
* context, followed by 8 bytes for
* the hash of the url being pointed to by the link, followed by 8
* bytes for the hash of "info:url_pointed_to_by_link".
* @var string
*/
var $doc_infos;
/**
* Length of $doc_infos as a string
* @var int
*/
var $docids_len;
/**
* This string is non-empty when shard is loaded and in its packed state.
* It consists of a sequence of posting records. Each posting
* consists of a offset into the document entries structure
* for a document containing the word this is the posting for,
* as well as the number of occurrences of that word in that document.
* @var string
*/
var $word_docs;
/**
* Length of $word_docs as a string
* @var int
*/
var $word_docs_len;
/**
* Stores the array of word entries for this shard
* In the packed state, word entries consist of the word id,
* a generation number, an offset into the word_docs structure
* where the posting list for that word begins,
* and a length of this posting list. In the unpacked state
* each entry is a string of all the posting items for that word
* Periodically data in this words array is flattened to the word_postings
* string which is a more memory efficient was of storing data in PHP
* @var array
*/
var $words;
/**
* Stores length of the words array in the shard on disk. Only set if
* we're in $read_only_from_disk mode
*
* @var int
*/
var $words_len;
/**
* An array representing offsets into the words dictionary of the index of
* the first occurrence of a two byte prefix of a word_id.
*
* @var array
*/
var $prefixes;
/**
* Length of the prefix index into the dictionary of the shard
*
* @var int
*/
var $prefixes_len;
/**
* This is supposed to hold the number of earlier shards, prior to the
* current shard.
* @var int
*/
var $generation;
/**
* This is supposed to hold the number of documents that a given shard can
* hold.
* @var int
*/
var $num_docs_per_generation;
/**
* Number of documents (not links) stored in this shard
* @var int
*/
var $num_docs;
/**
* Number of links (not documents) stored in this shard
* @var int
*/
var $num_link_docs;
/**
* Number of words stored in total in all documents in this shard
* @var int
*/
var $len_all_docs;
/**
* Number of words stored in total in all links in this shard
* @var int
*/
var $len_all_link_docs;
/**
* File handle for a shard if we are going to use it in read mode
* and not completely load it.
*
* @var resource
*/
var $fh;
/**
* An cached array of disk blocks for an index shard that has not
* been completely loaded into memory.
* @var array
*/
var $blocks;
/**
* Flag used to determined if this shard is going to be largely kept on
* disk and to be in read only mode. Otherwise, shard will assume to
* be completely held in memory and be read/writable.
* @var bool
*/
var $read_only_from_disk;
/**
* Keeps track of the packed/unpacked state of the word_docs list
*
* @var bool
*/
var $word_docs_packed;
/**
* Keeps track of the length of the shard as a file
*
* @var int
*/
var $file_len;
/**
* Number of document inserts since the last time word data was flattened
* to the word_postings string.
*/
var $last_flattened_words_count;
/**
* Used to hold word_id, posting_len, posting triples as a memory efficient
* string
* @var string
*/
var $word_postings;
/**
* Fraction of NUM_DOCS_PER_GENERATION document inserts before data
* from the words array is flattened to word_postings. (It will
* also be flattened during periodic index saves)
*/
const FLATTEN_FREQUENCY = 10000;
/**
* Bytes of tmp string allowed during flattenings
*/
const WORD_POSTING_COPY_LEN = 2000000;
/**
* Used to keep track of whether a record in document infos is for a
* document or for a link
*/
const LINK_FLAG = 0x800000;
/**
* Shard block size is 1<< this power
*/
const SHARD_BLOCK_POWER = 12;
/**
* Size in bytes of one block in IndexShard
*/
const SHARD_BLOCK_SIZE = 4096;
/**
* Header Length of an IndexShard (sum of its non-variable length fields)
*/
const HEADER_LENGTH = 40;
/**
* Length of the data portion of a word entry in bytes in the shard
*/
const WORD_DATA_LEN = 12;
/**
* Length of a word entry's key in bytes
*/
const WORD_KEY_LEN = 20;
/**
* Length of a key in a DOC ID.
*/
const DOC_KEY_LEN = 8;
/**
* Length of DOC ID.
*/
const DOC_ID_LEN = 24;
/**
* Length of one posting ( a doc offset occurrence pair) in a posting list
*/
const POSTING_LEN = 4;
/**
* Represents an empty prefix item
*/
const BLANK = "\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF";
/**
* Flag used to indicate that a word item should not be packed or unpacked
*/
const HALF_BLANK = "\xFF\xFF\xFF\xFF";
/**
* Represents an empty prefix item
*/
const STORE_FLAG = "\x80";
/**
* Makes an index shard with the given file name and generation offset
*
* @param string $fname filename to store the index shard with
* @param int $generation when returning documents from the shard
* pretend there ar ethis many earlier documents
* @param bool $read_only_from_disk used to determined if this shard is
* going to be largely kept on disk and to be in read only mode.
* Otherwise, shard will assume to be completely held in memory and be
* read/writable.
*/
function __construct($fname, $generation = 0,
$num_docs_per_generation = NUM_DOCS_PER_GENERATION,
$read_only_from_disk = false)
{
parent::__construct($fname, -1);
$this->hash_name = crawlHash($fname);
$this->generation = $generation;
$this->num_docs_per_generation = $num_docs_per_generation;
$this->word_docs = "";
$this->word_postings = "";
$this->words_len = 0;
$this->word_docs_len = 0;
$this->last_flattened_words_count = 0;
$this->words = array();
$this->docids_len = 0;
$this->doc_infos = "";
$this->num_docs = 0;
$this->num_link_docs = 0;
$this->len_all_docs = 0;
$this->len_all_link_docs = 0;
$this->blocks = array();
$this->fh = NULL;
$this->read_only_from_disk = $read_only_from_disk;
$this->word_docs_packed = false;
$this->blocks_words= array();
}
/**
* Add a new document to the index shard with the given summary offset.
* Associate with this document the supplied list of words and word counts.
* Finally, associate the given meta words with this document.
*
* @param string $doc_keys a string of concatenated keys for a document
* to insert. Each key is assumed to be a string of DOC_KEY_LEN many
* bytes. This whole set of keys is viewed as fixing one document.
* @param int $summary_offset its offset into the word archive the
* document's data is stored in
* @param array $word_lists (word => array of word positions in doc)
* @param array $meta_ids meta words to be associated with the document
* an example meta word would be filetype:pdf for a PDF document.
* @param array $materialized_metas
* @param bool $is_doc flag used to indicate if what is being sored is
* a document or a link to a document
* @param mixed $rank either false if not used, or a 4 bit estimate of the
* rank of this document item
* @return bool success or failure of performing the add
*/
function addDocumentWords($doc_keys, $summary_offset, $word_lists,
$meta_ids = array(), $materialized_metas = array(), $is_doc = false,
$rank = false)
{
if($this->word_docs_packed == true) {
$this->words = array();
$this->word_docs = "";
$this->word_docs_packed = false;
}
$doc_len = 0;
$link_doc_len = 0;
$len_key = strlen($doc_keys);
$num_keys = floor($len_key/self::DOC_KEY_LEN);
if($num_keys * self::DOC_KEY_LEN != $len_key) return false;
if($num_keys % 2 == 0 ) {
$doc_keys .= self::BLANK; //want to keep docids_len divisible by 16
}
$summary_offset_string = packInt($summary_offset);
$added_len = strlen($summary_offset_string);
$this->doc_infos .= $summary_offset_string;
if($is_doc) {
$this->num_docs++;
} else { //link item
$this->num_link_docs++;
}
foreach($meta_ids as $meta_id) {
$word_lists[$meta_id] = array();
}
$meta_string = encodeMaterialMetas($meta_ids, $materialized_metas);
//using $this->docids_len divisible by 16
$doc_offset = $this->docids_len >> 4;
foreach($word_lists as $word => $position_list) {
$occurrences = count($position_list);
if(isset($position_list["cond_max"])) { //for now
$word_id = crawlHashPath($word,
$position_list["cond_max"], array(), array(), true);
unset($position_list["cond_max"]);
} else {
$word_id = crawlHashWord($word, true, $meta_string);
}
$store = packPosting($doc_offset, $position_list);
if(!isset($this->words[$word_id])) {
$this->words[$word_id] = $store;
} else {
$this->words[$word_id] .= $store;
}
if($occurrences > 0) {
if($is_doc == true) {
$doc_len += $occurrences;
} else {
$link_doc_len += $occurrences;
}
}
$this->word_docs_len += strlen($store);
}
$this->len_all_docs += $doc_len;
$this->len_all_link_docs += $link_doc_len;
$flags = ($is_doc) ? 0 : self::LINK_FLAG;
if($rank !== false) {
$rank &= 0x0f;
$rank <<= 19;
$flags += $rank;
}
$item_len = ($is_doc) ? $doc_len: $link_doc_len;
$len_num_keys = $this->packDoclenNum(($flags + $item_len), $num_keys);
$this->doc_infos .= $len_num_keys;
$added_len += strlen($len_num_keys);
$this->doc_infos .= $doc_keys;
$added_len += strlen($doc_keys);
$this->docids_len += $added_len;
return true;
}
/**
* Returns the first offset, last offset, and number of documents the
* word occurred in for this shard. The first offset (similarly, the last
* offset) is the byte offset into the word_docs string of the first
* (last) record involving that word.
*
* @param string $word_id id of the word one wants to look up
* @param bool $raw whether the id is our version of base64 encoded or not
* @param int $shift how many low order bits to drop from $word_id's
* when checking for a match
* @return array first offset, last offset, count, exact matching id (
* recall match can ignore low order shift bits)
*/
function getWordInfo($word_id, $raw = false, $shift = 0)
{
if($raw == false) {
//get rid of out modfied base64 encoding
$word_id = unbase64Hash($word_id);
}
$is_disk = $this->read_only_from_disk;
$word_item_len = self::WORD_KEY_LEN + self::WORD_DATA_LEN;
$word_key_len = self::WORD_KEY_LEN;
if($is_disk) {
$this->getShardHeader();
if(!isset($word_id[1])) {
return false;
}
$prefix = (ord($word_id[0]) << 8) + ord($word_id[1]);
$prefix_info = $this->getShardSubstring(
self::HEADER_LENGTH + 8 * $prefix, 8);
if($prefix_info == self::BLANK) {
return false;
}
list(,$offset, $high) = unpack("N*", $prefix_info);
$high--;
$start = self::HEADER_LENGTH + $this->prefixes_len + $offset;
} else {
if($this->word_docs_packed == false) {
$this->mergeWordPostingsToString();
$this->packWords(NULL);
$this->outputPostingLists();
}
$start = 0;
$high = (strlen($this->words) - $word_item_len)/$word_item_len;
}
$low = 0;
$check_loc = (($low + $high) >> 1);
do {
$old_check_loc = $check_loc;
if($is_disk) {
$word_string = $this->getShardSubstring($start +
$check_loc * $word_item_len, $word_item_len);
} else {
$word_string = substr($this->words, $start +
$check_loc * $word_item_len, $word_item_len);
}
if($word_string == false) {return false;}
$id = substr($word_string, 0, $word_key_len);
$cmp = compareWordHashes($word_id, $id, $shift);
if($cmp === 0) {
$tmp_info = $this->getWordInfoFromString(
substr($word_string, $word_key_len));
$tmp_info[] = $id;
return $tmp_info;
} else if ($cmp < 0) {
$high = $check_loc;
$check_loc = (($low + $check_loc) >> 1);
} else {
if($check_loc + 1 == $high) {
$check_loc++;
}
$low = $check_loc;
$check_loc = (($high + $check_loc) >> 1);
}
} while($old_check_loc != $check_loc);
return false;
}
/**
* Returns documents using the word_docs string (either as stored
* on disk or completely read in) of records starting
* at the given offset and using its link-list of records. Traversal of
* the list stops if an offset larger than $last_offset is seen or
* $len many doc's have been returned. Since $next_offset is passed by
* reference the value of $next_offset will point to the next record in
* the list (if it exists) after the function is called.
*
* @param int $start_offset of the current posting list for query term
* used in calculating BM25F.
* @param int &$next_offset where to start in word docs
* @param int $last_offset offset at which to stop by
* @param int $len number of documents desired
* @return array desired list of doc's and their info
*/
function getPostingsSlice($start_offset, &$next_offset, $last_offset, $len)
{
if(!$this->read_only_from_disk && !$this->word_docs_packed) {
$this->mergeWordPostingsToString();
$this->packWords(NULL);
$this->outputPostingLists();
}
$num_docs_so_far = 0;
$results = array();
/* wd_len is a kludgy fix because word_docs_len can get out of sync
when things are file-based and am still tracking down why
*/
$wd_len = (isset($this->file_len )) ?
$this->file_len - $this->docids_len : $this->word_docs_len;
$end = min($wd_len, $last_offset) >> 2;
$last = $last_offset >> 2;
$next = $next_offset >> 2;
$posting_end = $next;
$total_posting_len = 0;
$num_postings_so_far = 0;
do {
if($next > $end) {break;}
$posting_start = $next;
$posting = $this->getPostingAtOffset(
$next, $posting_start, $posting_end);
$total_posting_len += strlen($posting);
$num_postings_so_far++;
$next = $posting_end + 1;
$num_docs_or_links =
self::numDocsOrLinks($start_offset, $last_offset,
$total_posting_len/$num_postings_so_far);
list($doc_id, , $item) =
$this->makeItem($posting, $num_docs_or_links);
$results[$doc_id] = $item;
$num_docs_so_far += $next - $posting_start;
} while ($next <= $last && $num_docs_so_far < $len);
$next_offset = $next << 2;
return $results;
}
/**
* An upper bound on the number of docs or links represented by
* the start and ending integer offsets into a posting list.
*
* @param int $start_offset starting location in posting list
* @param int $last_offset ending location in posting list
* @param float $avg_posting_len number of bytes in an average posting
*
* @return int number of docs or links
*/
static function numDocsOrLinks($start_offset, $last_offset,
$avg_posting_len = 4)
{
return ceil(($last_offset - $start_offset) /$avg_posting_len);
}
/**
* Return (docid, item) where item has document statistics (summary offset,
* relevance, doc rank, and score) for the document give by the
* supplied posting, based on the the posting lists
* num docs with word, and the number of occurrences of the word in the doc.
* Returns the doc_id of the document
*
* @param string $posting a posting entry from some words posting list
* @param int $num_doc_or_links number of documents or links doc appears in
* @param int $occurs number of occurrences of the current word in
* the document. If nonzero, this overrides the number of occurrences
* in various parts of a document that would be determined by its
* position list. Typically, would only override for meta words.
*
* @return array ($doc_id, posting_stats_array) for posting
*/
function makeItem($posting, $num_doc_or_links, $occurs = 0)
{
$doc_key_len = self::DOC_KEY_LEN;
$offset = 0;
list($doc_index, $position_list) =
unpackPosting($posting, $offset);
$item[self::POSITION_LIST] = $position_list;
$doc_depth = log(($doc_index + 1) + (AVG_LINKS_PER_PAGE + 1) *
$this->num_docs_per_generation * $this->generation, 10);
$item[self::DOC_RANK] = number_format(10 - $doc_depth, PRECISION);
$doc_loc = $doc_index << 4;
list(, $item[self::SUMMARY_OFFSET], $doc_int) =
unpack("N*", $this->getDocInfoSubstring($doc_loc, $doc_key_len));
$num_keys = $doc_int & 255;
if($num_keys > 15) { /* shouldn't have more than this many keys
fighting index corruption
*/
$num_keys = 3;
}
$doc_id_len = ($num_keys > 3) ? self::DOC_ID_LEN : $num_keys *
$doc_key_len; /* original format allowed shorter doc ids,
keys might be used for other things than ranking */
$doc_len = ($doc_int >> 8);
$item[self::GENERATION] = $this->generation;
$is_doc = (($doc_len & self::LINK_FLAG) == 0) ? true : false;
if(!$is_doc) {
$doc_len &= (self::LINK_FLAG - 1);
}
$item[self::DOC_LEN] = $doc_len;
$item[self::IS_DOC] = $is_doc;
$item[self::PROXIMITY]=$this->computeProximity($position_list, $is_doc);
$occurrences = $this->weightedCount($position_list, $is_doc);
//override $occurrences if $occurs != 0
if($occurs != 0) {
$occurrences = array(
self::TITLE => 0,
self::DESCRIPTION => 0,
self::LINKS => 0);
if($is_doc) {
$occurrences[self::DESCRIPTION] = $occurs;
} else {
$occurrences[self::LINKS] = $occurs;
}
}
/*
for archive crawls we store rank as the 4 bits after the high order
bit
*/
$rank_mask = (0x0f) << 19;
$pre_rank = ($doc_len & $rank_mask);
if( $pre_rank > 0) {
$item[self::DOC_RANK] = $pre_rank >> 19;
$doc_len &= (2 << 19 - 1);
}
$skip_stats = false;
if($item[self::SUMMARY_OFFSET] == self::NEEDS_OFFSET_FLAG) {
$skip_stats = true;
$item[self::RELEVANCE] = 1;
$item[self::SCORE] = $item[self::DOC_RANK];
} else if($is_doc) {
$average_doc_len = $this->len_all_docs/$this->num_docs;
$num_docs = $this->num_docs;
$type_weight = 1;
} else {
$average_doc_len = ($this->num_link_docs != 0) ?
$this->len_all_link_docs/$this->num_link_docs : 0;
$num_docs = $this->num_link_docs;
$type_weight = floatval(LINK_WEIGHT);
}
if(!isset($item['KEY'])) {
$id_pos = $doc_loc + $doc_key_len;
$doc_id = $this->getDocInfoSubstring(
$id_pos, $doc_id_len);
if($num_keys > 3 && $is_doc) {
$user_rank_string = $this->getDocInfoSubstring(
$id_pos + $doc_id_len, ($num_keys - 3) * $doc_key_len);
$item[self::USER_RANKS] = array_values(
unpack("N*", $user_rank_string));
$last = count($item[self::USER_RANKS]);
if($last > 0 && $item[self::USER_RANKS][$last - 1] == 0) {
unset($item[self::USER_RANKS][$last - 1]);
}
}
} else {
$doc_id = $item['KEY'];
}
if(!$skip_stats) {
$item[self::RELEVANCE] = 0;
if($occurrences[self::TITLE] > 0) {
self::docStats($item, $occurrences[self::TITLE],
AD_HOC_TITLE_LENGTH,
$num_doc_or_links, AD_HOC_TITLE_LENGTH, $num_docs,
$this->num_docs + $this->num_link_docs,
floatval(TITLE_WEIGHT));
}
if($occurrences[self::DESCRIPTION] > 0) {
$average_doc_len =
max($average_doc_len - AD_HOC_TITLE_LENGTH, 1);
$doc_len = max($doc_len - AD_HOC_TITLE_LENGTH, 1);
self::docStats($item, $occurrences[self::DESCRIPTION],
$doc_len, $num_doc_or_links, $average_doc_len , $num_docs,
$this->num_docs + $this->num_link_docs,
floatval(DESCRIPTION_WEIGHT));
}
if($occurrences[self::LINKS] > 0) {
self::docStats($item, $occurrences[self::LINKS],
$doc_len, $num_doc_or_links, $average_doc_len , $num_docs,
$this->num_docs + $this->num_link_docs,
floatval(LINK_WEIGHT));
}
$aux_scores = 1;
if(isset($item[self::USER_RANKS])) {
foreach($item[self::USER_RANKS] as $score) {
$aux_scores *= $score/6553.6;
}
}
$item[self::SCORE] = $item[self::DOC_RANK]
* $item[self::RELEVANCE] * $aux_scores;
/*crude score not used for final
results */
}
return array($doc_id, $num_keys, $item);
}
/**
* Used to sum over the occurences in a position list counting with
* weight based on term location in the document
*
* @param array $position_list positions of term in item
* @param bool $is_doc whether the item is a document or a link
* @return array asscoiative array of document_part => weight count
* of occurrences of term in
*
*/
function weightedCount($position_list, $is_doc) {
$count = array(
self::TITLE => 0,
self::DESCRIPTION => 0,
self::LINKS => 0);
foreach($position_list as $position) {
if($is_doc) {
if($position < AD_HOC_TITLE_LENGTH) {
$count[self::TITLE] ++;
} else {
$count[self::DESCRIPTION]++;
}
} else {
$count[self::LINKS]++;
}
}
return $count;
}
/**
* Returns a proximity score for a single term based on its location in
* doc.
*
* @param array $position_list locations of term within item
* @param bool $is_doc whether the item is a document or not
* @return int a score for proximity
*/
function computeProximity($position_list, $is_doc) {
return (!$is_doc) ? floatval(LINK_WEIGHT): (isset($position_list[0]) &&
$position_list[0] < AD_HOC_TITLE_LENGTH) ?
floatval(TITLE_WEIGHT) : floatval(DESCRIPTION_WEIGHT);
}
/**
* Computes BM25F relevance and a score for the supplied item based
* on the supplied parameters.
*
* @param array &$item doc summary to compute a relevance and score for.
* Pass-by-ref so self::RELEVANCE and self::SCORE fields can be changed
* @param int $occurrences - number of occurences of the term in the item
* @param int $doc_len number of words in doc item represents
* @param int $num_doc_or_link number of links or docs containing the term
* @param float $average_doc_len average length of items in corpus
* @param int $num_docs either number of links or number of docs depending
* if item represents a link or a doc.
* @param int $total_docs_or_links number of docs or links in corpus
* @param float BM25F weight for this component (doc or link) of score
*/
static function docStats(&$item, $occurrences, $doc_len, $num_doc_or_links,
$average_doc_len, $num_docs, $total_docs_or_links, $type_weight)
{
$half = 0.5;
$doc_ratio = ($average_doc_len > 0) ? $doc_len/$average_doc_len : 0;
$pre_relevance = number_format(
3 * $occurrences/($occurrences + $half + 1.5* $doc_ratio),
PRECISION);
if($num_doc_or_links > $total_docs_or_links) {
$num_doc_or_links = 0.5 * $total_docs_or_links;
//this case shouldn't happen but do a sanity check
}
$num_term_occurrences = $num_doc_or_links *
$num_docs/($total_docs_or_links);
$IDF = log(($num_docs - $num_term_occurrences + $half) /
($num_term_occurrences + $half));
$item[self::RELEVANCE] += $half * $IDF * $pre_relevance * $type_weight;
}
/**
* Gets the posting closest to index $current in the word_docs string
* modifies the passed-by-ref variables $posting_start and
* $posting_end so they are the index of the the start and end of the
* posting
*
* @param int $current an index into the word_docs strings
* corresponds to a start search loc of $current * self::POSTING_LEN
* @param int &$posting_start after function call will be
* index of start of nearest posting to current
* @param int &$posting_end after function call will be
* index of end of nearest posting to current
* @return string the substring of word_docs corresponding to the posting
*/
function getPostingAtOffset($current, &$posting_start, &$posting_end)
{
$posting_start = $current;
$posting_end = $current;
$pword = $this->getWordDocsWord($current << 2);
$chr = ($pword >> 24) & 192;
if(!$chr) {
return packInt($pword);
}
$continue = $chr != 192;
while ($continue) {
$posting_start--;
$cpword = $this->getWordDocsWord($posting_start << 2);
$continue = ((($cpword >> 24) & 192) == 128);
}
while((($pword >> 24) & 192) > 64) {
$posting_end++;
$pword = $this->getWordDocsWord($posting_end << 2);
}
return $this->getWordDocsSubstring($posting_start << 2,
($posting_end - $posting_start + 1) << 2);
}
/**
* Returns the document index of the posting at offset $current in
* word_docs
* @param int $current an offset into the posting lists (word_docs)
* @return int the doc index of the pointed to posting
*/
function getDocIndexOfPostingAtOffset($current)
{
$current_offset = $current << 2;
$pword = $this->getWordDocsWord($current_offset);
$chr = (($pword >> 24) & 192);
if(!$chr) {
return docIndexModified9($pword);
}
$continue = $chr != 192;
while ($continue) {
$current_offset -= 4;
$pword = $this->getWordDocsWord($current_offset);
$continue = ((($pword >> 24) & 192) == 128);
}
return docIndexModified9($pword);
}
/**
* Finds the first posting offset between $start_offset and $end_offset
* of a posting that has a doc_offset bigger than or equal to $doc_offset
* This is implemented using a galloping search (double offset till
* get larger than binary search).
*
* @param int $start_offset first posting to consider
* @param int $end_offset last posting before give up
* @param int $doc_offset document offset we want to be greater than or
* equal to
*
* @return array (int offset to next posting, doc_offset for this post)
*/
function nextPostingOffsetDocOffset($start_offset, $end_offset,
$doc_offset)
{
$doc_index = $doc_offset >> 4;
$end = $end_offset >> 2;
$post_doc_index = $this->getDocIndexOfPostingAtOffset($end);
if($doc_index > $post_doc_index) { //fail fast
return false;
} else if ($doc_index == $post_doc_index) {
return array($end << 2, $post_doc_index << 4);
}
$current = $start_offset >> 2;
$post_doc_index = $this->gallopPostingOffsetDocOffset($current,
$doc_index, $end);
if($doc_index == $post_doc_index) {
return array($current << 2, $post_doc_index << 4);
}
$low = $start_offset >> 2;
$high = $end;
do {
$post_doc_index = $this->getDocIndexOfPostingAtOffset($current);
if($doc_index > $post_doc_index) {
$low = $current;
if($current >= $end) {
return false;
} else {
if($current + 1 == $high) {
$current++;
$low = $current;
}
$current = (($low + $high) >> 1);
}
} else if($doc_index < $post_doc_index) {
if($low == $current) {
return array($current << 2, $post_doc_index << 4);
}
$high = $current;
$current = (($low + $high) >> 1);
} else {
return array($current << 2, $post_doc_index << 4);
}
} while($current <= $end);
return false;
}
/**
* Performs a galloping search (double forward jump distance each failure
* step) forward in a posting list from
* position $current forward until either $end is reached or a
* posting with document index bigger than $doc_index is found
*
* @param int &$current current posting offset into posting list
* @param int $doc_index document index want bigger than or equal to
* @param int $end last index of posting list
* @return int document index bigger than or equal to $doc_index. Since
* $current points at the posting this occurs for if found, no success
* by whether $current > $end.
*/
function gallopPostingOffsetDocOffset(&$current, $doc_index, $end)
{
$stride = 32;
do {
$post_doc_index = $this->getDocIndexOfPostingAtOffset($current);
if($doc_index <= $post_doc_index) {
return $post_doc_index;
}
$current += $stride;
$stride <<= 1;
} while($current <= $end);
$current = $end;
return $post_doc_index;
}
/**
* Given an offset of a posting into the word_docs string, looks up
* the posting there and computes the doc_offset stored in it.
*
* @param int $offset byte/char offset into the word_docs string
* @return int a document byte/char offset into the doc_infos string
*/
function docOffsetFromPostingOffset($offset) {
$doc_index = $this->getDocIndexOfPostingAtOffset($offset >> 2);
return ($doc_index << 4);
}
/**
* Returns $len many documents which contained the word corresponding to
* $word_id (only works for loaded shards)
*
* @param string $word_id key to look up documents for
* @param int number of documents desired back (from start of word linked
* list).
* @return array desired list of doc's and their info
*/
function getPostingsSliceById($word_id, $len)
{
$results = array();
$info = $this->getWordInfo($word_id, true);
if($info !== false) {
list($first_offset, $last_offset,
$num_docs_or_links) = $info;
$results = $this->getPostingsSlice($first_offset,
$first_offset, $last_offset, $len);
}
return $results;
}
/**
* Adds the contents of the supplied $index_shard to the current index
* shard
*
* @param object $index_shard the shard to append to the current shard
*/
function appendIndexShard($index_shard)
{
crawlLog("Appending index shard to current..");
if($this->word_docs_packed == true) {
$this->words = array();
$this->word_docs = "";
$this->word_docs_packed = false;
}
if($index_shard->word_docs_packed == true) {
crawlLog("Unpacking index shard word docs..");
$index_shard->unpackWordDocs();
crawlLog("..done.");
}
crawlLog("Concatenate index document info maps..");
$this->doc_infos .= $index_shard->doc_infos;
crawlLog("..done.");
crawlLog("Start processing the appended index shard's posting lists..");
$two_doc_len = 2 * self::DOC_KEY_LEN;
$num_words = count($index_shard->words);
$word_cnt = 0;
foreach($index_shard->words as $word_id => $postings) {
// update doc offsets for newly added docs
$add_len_flag = false;
$postings_len = strlen($postings);
if($postings_len > 0 && ($postings_len != $two_doc_len ||
strncmp($postings, self::HALF_BLANK, self::POSTING_LEN) != 0)) {
$new_postings = addDocIndexPostings($postings,
($this->docids_len >> 4));
$add_len_flag = true;
} else {
$new_postings = $postings;
}
$new_postings_len = strlen($new_postings);
if(!isset($this->words[$word_id])) {
$this->words[$word_id] = $new_postings;
} else {
$this->words[$word_id] .= $new_postings;
}
if($add_len_flag) {
$this->word_docs_len += $new_postings_len;
}
crawlTimeoutLog(".. still appending index shard words. At word: %s".
" of %s.", $word_cnt, $num_words);
$word_cnt++;
}
crawlLog("..done appending index shard words.");
$this->docids_len += $index_shard->docids_len;
$this->num_docs += $index_shard->num_docs;
$this->num_link_docs += $index_shard->num_link_docs;
$this->len_all_docs += $index_shard->len_all_docs;
$this->len_all_link_docs += $index_shard->len_all_link_docs;
crawlLog("Finishing index append...Mem:".memory_get_usage());
if($this->num_docs - $this->last_flattened_words_count >
self::FLATTEN_FREQUENCY) {
crawlLog("...Post Append Flattening Index Word Postings. Mem".
memory_get_usage());
$this->mergeWordPostingsToString();
crawlLog("...Flattened Index Word Postings. Mem:".
memory_get_usage());
}
}
/**
* Used to flatten the words associative array to a more memory
* efficient word_postings string.
*
* $this->words is an associative array with associations
* wordid => postinglistforid
* this format is relatively wasteful of memory
*
* $this->word_postings is a string in the format
* wordid1len1postings1wordid2len2postings2 ...
* wordids are lex ordered. This is more memory efficient ad the
* former relies on the more wasteful php implementation fo associative
* arrays.
*
* mergeWordPostingsToString converts the former format to the latter
* for each of the current wordids. This words is then set to array();
* Note before this operation is done $this->word_postings might have
* data from earlier times mergeWordPostingsToString was called, in which
* case the behavior is controlled by $replace.
*
* @param bool $replace whether to overwrite existing word_id postings
* (true) or to append (false)
*/
function mergeWordPostingsToString($replace = false)
{
if($this->word_docs_packed) {
return;
}
crawlLog("Merge index shard postings to string to save memory.");
ksort($this->words, SORT_STRING);
$tmp_string = "";
$offset = 0;
$write_offset = 0;
$len = strlen($this->word_postings);
$key_len = self::WORD_KEY_LEN;
$posting_len = self::POSTING_LEN;
$item_len = $key_len + $posting_len;
$num_words = count($this->words);
$i = 0;
foreach($this->words as $word_id => $postings) {
$cmp = -1;
while($cmp < 0 && $offset + $item_len <= $len) {
crawlTimeoutLog("..merging index word postings to string ..".
" processing %s of %s at offset %s less than %s", $i,
$num_words, $offset, $len);
$key = substr($this->word_postings, $offset, $key_len);
$pack_key_posts_len = substr(
$this->word_postings, $offset + $key_len, $posting_len);
$key_posts_len = unpackInt($pack_key_posts_len);
$key_postings = substr($this->word_postings,
$offset + $item_len, $key_posts_len);
$word_id_posts_len = strlen($postings);
$cmp = strcmp($key, $word_id);
if($cmp == 0) {
if($replace) {
$tmp_string .= $key .
packInt($word_id_posts_len) . $postings;
} else {
$tmp_string .= $key .
packInt($key_posts_len + $word_id_posts_len) .
$key_postings . $postings;
$offset += $item_len + $key_posts_len;
}
} else if ($cmp < 0) {
$tmp_string .= $key .$pack_key_posts_len. $key_postings;
$offset += $item_len + $key_posts_len;
} else {
$tmp_string .= $word_id .
packInt($word_id_posts_len). $postings;
}
$tmp_len = strlen($tmp_string);
$copy_data_len = min(self::WORD_POSTING_COPY_LEN, $tmp_len);
$copy_to_len = min($offset - $write_offset,
$len - $write_offset);
if($copy_to_len > $copy_data_len) {
charCopy($tmp_string, $this->word_postings, $write_offset,
$copy_data_len, "merge index charCopy 1");
$write_offset += $copy_data_len;
$tmp_string = substr($tmp_string, $copy_data_len);
}
}
crawlTimeoutLog("..outer loop merge index postings to string ..".
" processing %s of %s.", $i, $num_words);
if($offset + $item_len > $len) {
$word_id_posts_len = strlen($postings);
if($write_offset < $len) {
$tmp_len = strlen($tmp_string);
$copy_data_len = $len - $write_offset;
if($tmp_len < $copy_data_len) { // this case shouldn't occur
$this->word_postings =
substr($this->word_postings, 0, $write_offset);
$this->word_postings .= $tmp_string;
} else {
charCopy($tmp_string, $this->word_postings,
$write_offset, $copy_data_len,
"merge index charCopy 2");
$tmp_string = substr($tmp_string, $copy_data_len);
$this->word_postings .= $tmp_string;
}
$tmp_string = "";
$write_offset = $len;
}
$this->word_postings .=
$word_id . packInt($word_id_posts_len). $postings;
}
$i++;
}
crawlLog("..Merge Index Posting Final Copy");
$this->words = array();
// garbage collection may take a while, call with true so don't time out
CrawlDaemon::processHandler(true);
if($tmp_string != "") {
$tmp_len = strlen($tmp_string);
$copy_data_len = $offset - $write_offset;
$pad_len = $tmp_len - $copy_data_len;
$pad = str_pad("", $pad_len, "@");
crawlLog("..Merge Index Posting Final Copy -- 1");
$this->word_postings .= $pad;
crawlLog("..Merge Index Posting Final Copy -- 2");
for($j = $len + $pad_len - 1,
$k = $len - 1; $k >= $offset; $j--, $k--) {
crawlTimeoutLog("..still in merge index final copy");
$this->word_postings[$j] = "" . $this->word_postings[$k];
/*way slower if directly
assign!!! PHP is crazy*/
}
charCopy($tmp_string, $this->word_postings,
$write_offset, $tmp_len,
"merge index charCopy 3");
}
$this->last_flattened_words_count = $this->num_docs;
crawlLog("..Done Merge Index Posting Final Copy");
}
/**
* Changes the summary offsets associated with a set of doc_ids to new
* values. This is needed because the fetcher puts documents in a
* shard before sending them to a queue_server. It is on the queue_server
* however where documents are stored in the IndexArchiveBundle and
* summary offsets are obtained. Thus, the shard needs to be updated at
* that point. This function should be called when shard unpacked
* (we check and unpack to be on the safe side).
*
* @param array $docid_offsets a set of doc_id associated with a
* new_doc_offset.
*/
function changeDocumentOffsets($docid_offsets)
{
if($this->word_docs_packed == true) {
$this->words = array();
$this->word_docs = "";
$this->word_docs_packed = false;
}
$docids_len = $this->docids_len;
$doc_key_len = self::DOC_KEY_LEN;
$row_len = $doc_key_len;
$posting_len = self::POSTING_LEN;
$num_items = floor($docids_len/$row_len);
$item_cnt = 0;
crawlTimeoutLog(true);
for($i = 0 ; $i < $docids_len; $i += $row_len) {
crawlTimeoutLog("..still changing document offsets. At" .
" document %s of %s.", $item_cnt, $num_items);
$item_cnt++;
$doc_info_string = $this->getDocInfoSubstring($i,
$doc_key_len);
list($offset, $doc_len_info) = array_values(unpack("N*",
$doc_info_string));
list($doc_len, $num_keys) =
$this->unpackDoclenNum($doc_len_info);
$doc_id_len = ($num_keys > 3) ? self::DOC_ID_LEN: $num_keys *
$doc_key_len;
$key_count = ($num_keys % 2 == 0) ? $num_keys + 2: $num_keys + 1;
$row_len = $doc_key_len * ($key_count);
$id = substr($this->doc_infos, $i + $doc_key_len,
$doc_id_len); /* id is only three keys of the list of keys,
remaining keys used for ranker */
if(isset($docid_offsets[$id])) {
charCopy(packInt($docid_offsets[$id]), $this->doc_infos,
$i, $posting_len);
} else if($offset == self::NEEDS_OFFSET_FLAG) {
crawlLog("Document:".toHexString($id)." still needs offset");
}
}
}
/**
* Save the IndexShard to its filename
*
* @param bool $to_string whether output should be written to a string
* rather than the default file location
* @param bool $with_logging whether log messages should be written
* as the shard save progresses
* @return string serialized shard if output was to string else empty
* string
*/
function save($to_string = false, $with_logging = false)
{
$out = "";
$this->mergeWordPostingsToString();
if($with_logging) {
crawlLog("Saving index shard .. done merge postings to string");
}
$this->prepareWordsAndPrefixes($with_logging);
if($with_logging) {
crawlLog("Saving index shard .. make prefixes");
}
$header = pack("N*", $this->prefixes_len ,
$this->words_len,
$this->word_docs_len,
$this->docids_len,
$this->generation,
$this->num_docs_per_generation,
$this->num_docs,
$this->num_link_docs,
$this->len_all_docs,
$this->len_all_link_docs);
if($with_logging) {
crawlLog("Saving index shard .. packed header");
}
if($to_string) {
$out = $header;
$this->packWords(NULL);
$out .= $this->words;
$this->outputPostingLists(NULL, $with_logging);
$out .= $this->word_docs;
$out .= $this->doc_infos;
} else {
$fh = fopen($this->filename, "wb");
fwrite($fh, $header);
fwrite($fh, $this->prefixes);
$this->packWords($fh, $with_logging);
if($with_logging) {
crawlLog("Saving index shard .. wrote dictionary");
}
$this->outputPostingLists($fh, $with_logging);
if($with_logging) {
crawlLog("Saving index shard .. wrote postings lists");
}
fwrite($fh, $this->doc_infos);
fclose($fh);
}
if($with_logging) {
crawlLog("Saving index shard .. wrote doc map. Done save");
}
// clean up by returning to state where could add more docs
$this->words = array();
$this->word_docs = "";
$this->prefixes = "";
$this->word_docs_packed = false;
return $out;
}
/**
* Computes the prefix string index for the current words array.
* This index gives offsets of the first occurrences of the lead two char's
* of a word_id in the words array. This method assumes that the word
* data is already in >word_postings
* @param bool $with_logging whether log messages should be written
* as progresses
*/
function prepareWordsAndPrefixes($with_logging = false)
{
$word_item_len = IndexShard::WORD_KEY_LEN + IndexShard::WORD_DATA_LEN;
$key_len = self::WORD_KEY_LEN;
$posting_len = self::POSTING_LEN;
$this->words_len = 0;
$word_postings_len = strlen($this->word_postings);
$pos = 0;
$tmp = array();
$offset = 0;
$num_words = 0;
$old_prefix = false;
while($pos < $word_postings_len) {
if($with_logging) {
crawlTimeoutLog("..Outputting to position %s of" .
" %s of prefixes.", $pos, $word_postings_len);
}
$this->words_len += $word_item_len;
$first = substr($this->word_postings, $pos, $key_len);
$post_len = unpackInt(substr($this->word_postings,
$pos + $key_len, $posting_len));
$pos += $key_len + $posting_len + $post_len;
$prefix = (ord($first[0]) << 8) + ord($first[1]);
if($old_prefix === $prefix) {
$num_words++;
} else {
if($old_prefix !== false) {
$tmp[$old_prefix] = pack("N*", $offset, $num_words);
$offset += $num_words * $word_item_len;
}
$old_prefix = $prefix;
$num_words = 1;
}
}
$tmp[$old_prefix] = pack("N*", $offset, $num_words);
$num_prefixes = 2 << 16;
$this->prefixes = "";
for($i = 0; $i < $num_prefixes; $i++) {
if(isset($tmp[$i])) {
$this->prefixes .= $tmp[$i];
} else {
$this->prefixes .= self::BLANK;
}
}
$this->prefixes_len = strlen($this->prefixes);
}
/**
* Posting lists are initially stored associated with a word as a key
* value pair. The merge operation then merges them these to a string
* help by word_postings. packWords separates words from postings.
* After being applied words is a string consisting of
* triples (as concatenated strings) word_id, start_offset, end_offset.
* The offsets refer to integers offsets into a string $this->word_docs
* Finally, if a file handle is given, it writes the word dictionary out
* to the file as a long string. This function assumes
* mergeWordPostingsToString has just been called.
*
* @param resource $fh a file handle to write the dictionary to, if desired
* @param bool $with_logging whether to write progress log messages every
* 30 seconds
*/
function packWords($fh = NULL, $with_logging = false)
{
if($this->word_docs_packed) {
return;
}
$word_item_len = IndexShard::WORD_KEY_LEN + IndexShard::WORD_DATA_LEN;
$key_len = self::WORD_KEY_LEN;
$posting_len = self::POSTING_LEN;
$this->word_docs_len = 0;
$this->words = "";
$total_out = "";
$word_postings_len = strlen($this->word_postings);
$pos = 0;
$two_doc_len = 2 * self::DOC_KEY_LEN;
while($pos < $word_postings_len) {
if($with_logging) {
crawlTimeoutLog("..packing index shard words at %s of %s.",
$pos, $word_postings_len);
}
$word_id = substr($this->word_postings, $pos, $key_len);
$len = unpackInt(substr($this->word_postings,
$pos + $key_len, $posting_len));
$postings = substr($this->word_postings,
$pos + $key_len + $posting_len, $len);
$pos += $key_len + $posting_len + $len;
/*
we pack generation info to make it easier to build the global
dictionary
*/
if($len != $two_doc_len ||
strncmp($postings, self::HALF_BLANK, self::POSTING_LEN) != 0) {
$out = pack("N*",$this->generation, $this->word_docs_len, $len);
$this->word_docs_len += $len;
$this->words .= $word_id . $out;
} else {
$out = substr($postings,
self::POSTING_LEN, $word_item_len);
$out[0] = chr((0x80 | ord($out[0])));
$this->words .= $word_id . $out;
}
}
if($fh != NULL) {
fwrite($fh, $this->words);
}
$this->words_len = strlen($this->words);
$this->word_docs_packed = true;
}
/**
* Used to convert the word_postings string into a word_docs string
* or if a file handle is provided write out the word_docs sequence
* of postings to the provided file handle.
*
* @param resource $fh a filehandle to write to
* @param bool $with_logging whether to log progress
*/
function outputPostingLists($fh = NULL, $with_logging = false)
{
$word_item_len = IndexShard::WORD_KEY_LEN + IndexShard::WORD_DATA_LEN;
$key_len = self::WORD_KEY_LEN;
$posting_len = self::POSTING_LEN;
$this->word_docs = "";
$total_out = "";
$word_postings_len = strlen($this->word_postings);
$pos = 0;
$tmp_string = "";
$tmp_len = 0;
$two_doc_len = 2 * self::DOC_KEY_LEN;
while($pos < $word_postings_len) {
if($with_logging) {
crawlTimeoutLog("..Outputting to position %s of" .
" %s in posting lists.", $pos,
$word_postings_len);
}
$word_id = substr($this->word_postings, $pos, $key_len);
$len = unpackInt(substr($this->word_postings,
$pos + $key_len, $posting_len));
$postings = substr($this->word_postings,
$pos + $key_len + $posting_len, $len);
$pos += $key_len + $posting_len + $len;
if($len != $two_doc_len ||
strncmp($postings, self::HALF_BLANK, self::POSTING_LEN) != 0) {
if($fh != NULL) {
if($tmp_len < self::SHARD_BLOCK_SIZE) {
$tmp_string .= $postings;
$tmp_len += $len;
} else {
fwrite($fh, $tmp_string);
$tmp_string = $postings;
$tmp_len = $len;
}
} else {
$this->word_docs .= $postings;
}
}
}
if($tmp_len > 0) {
if($fh == NULL ) {
$this->word_docs .= $tmp_string;
} else {
fwrite($fh, $tmp_string);
}
}
}
/**
* Takes the word docs string and splits it into posting lists which are
* assigned to particular words in the words dictionary array.
* This method is memory expensive as it briefly has essentially
* two copies of what's in word_docs.
*/
function unpackWordDocs()
{
if(!$this->word_docs_packed) {
return;
}
$num_lists = count($this->words);
$cnt = 0;
foreach($this->words as $word_id => $postings_info) {
/* we are ignoring the first four bytes which contains
generation info
*/
crawlTimeoutLog("..still unpacking index posting lists. At" .
" list %s of %s.", $cnt, $num_lists);
if((ord($postings_info[0]) & 0x80) > 0 ) {
$postings_info[0] = chr(ord($postings_info[0]) - 0x80);
$postings_info = self::HALF_BLANK . $postings_info;
$this->words[$word_id] = $postings_info;
} else {
$tmp = unpack("N*", substr($postings_info, 4,
8));
if(!isset($tmp[2])) {continue; }
list(, $offset, $len) = $tmp;
$postings = substr($this->word_docs, $offset, $len);
$this->words[$word_id] = $postings;
}
$cnt++;
}
unset($this->word_docs);
$this->word_docs_packed = false;
}
/**
* From disk gets $len many bytes starting from $offset in the word_docs
* strings
*
* @param $offset byte offset to begin getting data out of disk-based
* word_docs
* @param $len number of bytes to get
* @return desired string
*/
function getWordDocsSubstring($offset, $len)
{
if($this->read_only_from_disk) {
return $this->getShardSubstring($this->word_doc_offset + $offset,
$len);
}
return substr($this->word_docs, $offset, $len);
}
/**
* Reads 32 bit word as an unsigned int from the offset given in the
* word_docs string in the sahrd
* @param int $offset a byte offset into the word_docs string
*/
function getWordDocsWord($offset)
{
if($this->read_only_from_disk) {
return $this->getShardWord($this->word_doc_offset + $offset);
}
return unpackInt(substr($this->word_docs, $offset, 4));
}
/**
* From disk gets $len many bytes starting from $offset in the doc_infos
* strings
*
* @param $offset byte offset to begin getting data out of disk-based
* doc_infos
* @param $len number of bytes to get
* @return desired string
*/
function getDocInfoSubstring($offset, $len)
{
if($this->read_only_from_disk) {
return $this->getShardSubstring(
$this->doc_info_offset + $offset, $len, false);
}
return substr($this->doc_infos, $offset, $len);
}
/**
* Gets from Disk Data $len many bytes beginning at $offset from the
* current IndexShard
*
* @param int $offset byte offset to start reading from
* @param int $len number of bytes to read
* @param bool $cache whether to cache disk blocks read from disk
* @return string data fromthat location in the shard
*/
function getShardSubstring($offset, $len, $cache = true)
{
$block_offset = ($offset >> self::SHARD_BLOCK_POWER)
<< self::SHARD_BLOCK_POWER;
$start_loc = $offset - $block_offset;
//if all in one block do it quickly
if($start_loc + $len < self::SHARD_BLOCK_SIZE) {
return substr($this->readBlockShardAtOffset($block_offset, $cache),
$start_loc, $len);
}
// otherwise, this loop is slower, but handles general case
$data = $this->readBlockShardAtOffset($block_offset, $cache);
if($data === false) {return "";}
$substring = substr($data, $start_loc);
$block_size = self::SHARD_BLOCK_SIZE;
$block_offset += $block_size;
while (strlen($substring) < $len) {
$data = $this->readBlockShardAtOffset($block_offset, $cache);
if($data === false) {return $substring;}
$block_offset += $block_size;
$substring .= $data;
}
return substr($substring, 0, $len);
}
/**
* Reads 32 bit word as an unsigned int from the offset given in the shard
*
* @param int $offset a byte offset into the shard
* @return int desired word or false
*/
function getShardWord($offset)
{
if(isset($this->blocks_words[$offset])) {
return $this->blocks_words[$offset];
}
if($this->readBlockShardAtOffset(($offset >> self::SHARD_BLOCK_POWER) <<
self::SHARD_BLOCK_POWER)) {
return $this->blocks_words[$offset];
} else {
return false;
}
}
/**
* Reads SHARD_BLOCK_SIZE from the current IndexShard's file beginning
* at byte offset $bytes
*
* @param int $bytes byte offset to start reading from
* @param bool $cache whether to cache disk blocks that have been read to
* RAM
* @return &string data fromIndexShard file
*/
function readBlockShardAtOffset($bytes, $cache = true)
{
if(isset($this->blocks[$bytes])) {
return $this->blocks[$bytes];
}
if($this->fh === NULL) {
$this->fh = fopen($this->filename, "rb");
if($this->fh === false) return false;
$this->file_len = filesize($this->filename);
}
if($bytes >= $this->file_len) {
return false;
}
$seek = fseek($this->fh, $bytes, SEEK_SET);
if($seek < 0) {
return false;
}
if(!$cache) {
return fread($this->fh, self::SHARD_BLOCK_SIZE);
}
$this->blocks[$bytes] = fread($this->fh, self::SHARD_BLOCK_SIZE);
$tmp = & $this->blocks[$bytes];
$this->blocks_words += array_combine(
range($bytes, $bytes + strlen($tmp) - 1, 4),
unpack("N*", $tmp));
return $tmp;
}
/**
* If not already loaded, reads in from disk the fixed-length'd field
* variables of this IndexShard ($this->words_len, etc)
*/
function getShardHeader()
{
if(isset($this->num_docs) && $this->num_docs > 0) {
return; // if $this->num_docs > 0 assume have read in
}
$header = substr($this->readBlockShardAtOffset(0, false),
0, self::HEADER_LENGTH);
self::headerToShardFields($header, $this);
$this->doc_info_offset = $this->file_len - $this->docids_len;
}
/**
* Used to store the length of a document as well as the number of
* key components in its doc_id as a packed int (4 byte string)
*
* @param int $doc_len number of words in the document
* @param int $num_keys number of keys that are used to make up its doc_id
* @return string packed int string representing these two values
*/
static function packDoclenNum($doc_len, $num_keys)
{
return packInt(($doc_len << 8) + $num_keys);
}
/**
* Used to extract from a 32 bit unsigned int,
* a pair which represents the length of a document together with the
* number of keys in its doc_id
*
* @param int $doc_info integer to unpack
* @return array pair (number of words in the document,
* number of keys that are used to make up its doc_id)
*/
static function unpackDoclenNum($doc_info)
{
$num_keys = $doc_info & 255;
$doc_len = ($doc_info >> 8);
return array($doc_len, $num_keys);
}
/**
* Converts $str into 3 ints for a first offset into word_docs,
* a last offset into word_docs, and a count of number of docs
* with that word.
*
* @param string $str
* @param bool $include_generation
* @return array of these three or four int's
*/
static function getWordInfoFromString($str, $include_generation = false)
{
list(, $generation, $first_offset, $len) = unpack("N*", $str);
$last_offset = $first_offset + $len - self::POSTING_LEN;
$count = $len >> 2;
if($include_generation) {
return array($generation, $first_offset, $last_offset, $count);
}
return array($first_offset, $last_offset, $count);
}
/**
* Load an IndexShard from a file or string
*
* @param string $fname the name of the file to the IndexShard from/to
* @param string &$data stringified shard data to load shard from. If NULL
* then the data is loaded from the $fname if possible
* @return object the IndexShard loaded
*/
static function load($fname, &$data = NULL)
{
crawlLog("Loading index shard $fname");
$shard = new IndexShard($fname);
if($data === NULL) {
$fh = fopen($fname, "rb");
$shard->file_len = filesize($fname);
$header = fread($fh, self::HEADER_LENGTH);
} else {
$shard->file_len = strlen($data);
$header = substr($data, 0, self::HEADER_LENGTH);
$pos = self::HEADER_LENGTH;
}
self::headerToShardFields($header, $shard);
crawlLog("..done reading index shard header");
if($data === NULL) {
if(!($shard->prefixes_len > 0 )) return NULL;
if(!($shard->words_len > 0 )) return NULL;
if(!($shard->word_docs_len > 0 )) return NULL;
if(!($shard->docids_len > 0 )) return NULL;
fread($fh, $shard->prefixes_len);
$words = fread($fh, $shard->words_len);
$shard->word_docs = fread($fh, $shard->word_docs_len);
$shard->doc_infos = fread($fh, $shard->docids_len);
fclose($fh);
} else {
$words = substr($data, $pos, $shard->words_len);
$pos += $shard->words_len;
$shard->word_docs = substr($data, $pos, $shard->word_docs_len);
$pos += $shard->word_docs_len;
$shard->doc_infos = substr($data, $pos, $shard->docids_len);
}
$pre_words_array = str_split($words, self::WORD_KEY_LEN +
self::WORD_DATA_LEN);
unset($words);
array_walk($pre_words_array, 'IndexShard::makeWords', $shard);
crawlLog("..done reading making index shard word structure");
$shard->word_docs_packed = true;
$shard->unpackWordDocs();
crawlLog("..done unpacking index shard posting lists");
return $shard;
}
/**
* Split a header string into a shards field variable
*
* @param string $header a string with packed shard header data
* @param object shard IndexShard to put data into
*/
static function headerToShardFields($header, $shard)
{
list(,
$shard->prefixes_len,
$shard->words_len,
$shard->word_docs_len,
$shard->docids_len,
$shard->generation,
$shard->num_docs_per_generation,
$shard->num_docs,
$shard->num_link_docs,
$shard->len_all_docs,
$shard->len_all_link_docs
) = unpack("N*", $header);
$shard->word_doc_offset = self::HEADER_LENGTH +
$shard->prefixes_len + $shard->words_len;
}
/**
* Callback function for load method. splits a word_key . word_info string
* into an entry in the passed shard $shard->words[word_key] = $word_info.
*
* @param string &value the word_key . word_info string
* @param int $key index in array - we don't use
* @param object $shard IndexShard to add the entry to word table for
*/
static function makeWords(&$value, $key, $shard)
{
$shard->words[substr($value, 0, self::WORD_KEY_LEN)] =
substr($value, self::WORD_KEY_LEN,
self::WORD_DATA_LEN);
}
}