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// shardkey.h
* Copyright (C) 2008 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
* 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 <>.
#pragma once
#include "../client/dbclient.h"
namespace mongo {
class Chunk;
/* A ShardKeyPattern is a pattern indicating what data to extract from the object to make the shard key from.
Analogous to an index key pattern.
class ShardKeyPattern {
ShardKeyPattern( BSONObj p = BSONObj() );
global min is the lowest possible value for this key
e.g. { num : MinKey }
BSONObj globalMin() const { return gMin; }
global max is the highest possible value for this key
BSONObj globalMax() const { return gMax; }
bool isGlobalMin( const BSONObj& k ) const {
return k.woCompare( globalMin() ) == 0;
bool isGlobalMax( const BSONObj& k ) const {
return k.woCompare( globalMax() ) == 0;
bool isGlobal( const BSONObj& k ) const {
return isGlobalMin( k ) || isGlobalMax( k );
/** compare shard keys from the objects specified
l < r negative
l == r 0
l > r positive
int compare( const BSONObj& l , const BSONObj& r ) const;
@return whether or not obj has all fields in this shard key pattern
ShardKey({num:1}).hasShardKey({ name:"joe", num:3 }) is true
bool hasShardKey( const BSONObj& obj ) const;
BSONObj key() const { return pattern; }
string toString() const;
BSONObj extractKey(const BSONObj& from) const;
bool partOfShardKey(const char* key ) const {
return pattern.hasField(key);
bool partOfShardKey(const string& key ) const {
return pattern.hasField(key.c_str());
* @return
* true if 'this' is a prefix (not necessarily contained) of 'otherPattern'.
bool isPrefixOf( const BSONObj& otherPattern ) const;
* @return BSONObj with _id and shardkey at front. May return original object.
BSONObj moveToFront(const BSONObj& obj) const;
BSONObj pattern;
BSONObj gMin;
BSONObj gMax;
/* question: better to have patternfields precomputed or not? depends on if we use copy constructor often. */
set<string> patternfields;
inline BSONObj ShardKeyPattern::extractKey(const BSONObj& from) const {
BSONObj k = from.extractFields(pattern);
uassert(13334, "Shard Key must be less than 512 bytes", k.objsize() < 512);
return k;
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