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// fts_index_format.cpp
/**
* Copyright (C) 2012 10gen Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include "mongo/platform/basic.h"
#include <third_party/murmurhash3/MurmurHash3.h>
#include "mongo/base/init.h"
#include "mongo/db/fts/fts_index_format.h"
#include "mongo/db/fts/fts_spec.h"
#include "mongo/util/hex.h"
#include "mongo/util/md5.hpp"
#include "mongo/util/mongoutils/str.h"
namespace mongo {
namespace fts {
using std::string;
using std::vector;
namespace {
BSONObj nullObj;
BSONElement nullElt;
// New in textIndexVersion 2.
// If the term is longer than 32 characters, it may
// result in the generated key being too large
// for the index. In that case, we generate a 64-character key
// from the concatenation of the first 32 characters
// and the hex string of the murmur3 hash value of the entire
// term value.
const size_t termKeyPrefixLengthV2 = 32U;
// 128-bit hash value expressed in hex = 32 characters
const size_t termKeySuffixLengthV2 = 32U;
const size_t termKeyLengthV2 = termKeyPrefixLengthV2 + termKeySuffixLengthV2;
// TextIndexVersion 3.
// If the term is longer than 256 characters, it may
// result in the generated key being too large
// for the index. In that case, we generate a 256-character key
// from the concatenation of the first 224 characters
// and the hex string of the md5 hash value of the entire
// term value.
const size_t termKeyPrefixLengthV3 = 224U;
// 128-bit hash value expressed in hex = 32 characters
const size_t termKeySuffixLengthV3 = 32U;
const size_t termKeyLengthV3 = termKeyPrefixLengthV3 + termKeySuffixLengthV3;
/**
* Returns size of buffer required to store term in index key.
* In version 1, terms are stored verbatim in key.
* In version 2 and above, terms longer than 32 characters are hashed and combined
* with a prefix.
*/
int guessTermSize(const std::string& term, TextIndexVersion textIndexVersion) {
if (TEXT_INDEX_VERSION_1 == textIndexVersion) {
return term.size();
} else if (TEXT_INDEX_VERSION_2 == textIndexVersion) {
if (term.size() <= termKeyPrefixLengthV2) {
return term.size();
}
return termKeyLengthV2;
} else {
invariant(TEXT_INDEX_VERSION_3 == textIndexVersion);
if (term.size() <= termKeyPrefixLengthV3) {
return term.size();
}
return termKeyLengthV3;
}
}
} // namespace
MONGO_INITIALIZER(FTSIndexFormat)(InitializerContext* context) {
BSONObjBuilder b;
b.appendNull("");
nullObj = b.obj();
nullElt = nullObj.firstElement();
return Status::OK();
}
void FTSIndexFormat::getKeys(const FTSSpec& spec, const BSONObj& obj, BSONObjSet* keys) {
int extraSize = 0;
vector<BSONElement> extrasBefore;
vector<BSONElement> extrasAfter;
// compute the non FTS key elements
for (unsigned i = 0; i < spec.numExtraBefore(); i++) {
BSONElement e = obj.getFieldDotted(spec.extraBefore(i));
if (e.eoo())
e = nullElt;
uassert(16675, "cannot have a multi-key as a prefix to a text index", e.type() != Array);
extrasBefore.push_back(e);
extraSize += e.size();
}
for (unsigned i = 0; i < spec.numExtraAfter(); i++) {
BSONElement e = obj.getFieldDotted(spec.extraAfter(i));
if (e.eoo())
e = nullElt;
extrasAfter.push_back(e);
extraSize += e.size();
}
TermFrequencyMap term_freqs;
spec.scoreDocument(obj, &term_freqs);
// create index keys from raw scores
// only 1 per string
uassert(16732,
mongoutils::str::stream() << "too many unique keys for a single document to"
<< " have a text index, max is " << term_freqs.size()
<< obj["_id"],
term_freqs.size() <= 400000);
long long keyBSONSize = 0;
const int MaxKeyBSONSizeMB = 4;
for (TermFrequencyMap::const_iterator i = term_freqs.begin(); i != term_freqs.end(); ++i) {
const string& term = i->first;
double weight = i->second;
// guess the total size of the btree entry based on the size of the weight, term tuple
int guess = 5 /* bson overhead */ + 10 /* weight */ + 8 /* term overhead */ +
/* term size (could be truncated/hashed) */
guessTermSize(term, spec.getTextIndexVersion()) + extraSize;
BSONObjBuilder b(guess); // builds a BSON object with guess length.
for (unsigned k = 0; k < extrasBefore.size(); k++) {
b.appendAs(extrasBefore[k], "");
}
_appendIndexKey(b, weight, term, spec.getTextIndexVersion());
for (unsigned k = 0; k < extrasAfter.size(); k++) {
b.appendAs(extrasAfter[k], "");
}
BSONObj res = b.obj();
verify(guess >= res.objsize());
keys->insert(res);
keyBSONSize += res.objsize();
uassert(16733,
mongoutils::str::stream()
<< "trying to index text where term list is too big, max is "
<< MaxKeyBSONSizeMB << "mb " << obj["_id"],
keyBSONSize <= (MaxKeyBSONSizeMB * 1024 * 1024));
}
}
BSONObj FTSIndexFormat::getIndexKey(double weight,
const string& term,
const BSONObj& indexPrefix,
TextIndexVersion textIndexVersion) {
BSONObjBuilder b;
BSONObjIterator i(indexPrefix);
while (i.more()) {
b.appendAs(i.next(), "");
}
_appendIndexKey(b, weight, term, textIndexVersion);
return b.obj();
}
void FTSIndexFormat::_appendIndexKey(BSONObjBuilder& b,
double weight,
const string& term,
TextIndexVersion textIndexVersion) {
verify(weight >= 0 && weight <= MAX_WEIGHT); // FTSmaxweight = defined in fts_header
// Terms are added to index key verbatim.
if (TEXT_INDEX_VERSION_1 == textIndexVersion) {
b.append("", term);
b.append("", weight);
}
// See comments at the top of file for termKeyPrefixLengthV2.
// Apply hash for text index version 2 to long terms (longer than 32 characters).
else if (TEXT_INDEX_VERSION_2 == textIndexVersion) {
if (term.size() <= termKeyPrefixLengthV2) {
b.append("", term);
} else {
union {
uint64_t hash[2];
char data[16];
} t;
uint32_t seed = 0;
MurmurHash3_x64_128(term.data(), term.size(), seed, t.hash);
string keySuffix = mongo::toHexLower(t.data, sizeof(t.data));
invariant(termKeySuffixLengthV2 == keySuffix.size());
b.append("", term.substr(0, termKeyPrefixLengthV2) + keySuffix);
}
b.append("", weight);
} else {
invariant(TEXT_INDEX_VERSION_3 == textIndexVersion);
if (term.size() <= termKeyPrefixLengthV3) {
b.append("", term);
} else {
string keySuffix = md5simpledigest(term);
invariant(termKeySuffixLengthV3 == keySuffix.size());
b.append("", term.substr(0, termKeyPrefixLengthV3) + keySuffix);
}
b.append("", weight);
}
}
}
}
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