1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
|
// balancer_policy.cpp
/**
* Copyright (C) 2010 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/>.
*/
#include "pch.h"
#include "config.h"
#include "../client/dbclient.h"
#include "../util/stringutils.h"
#include "../util/unittest.h"
#include "balancer_policy.h"
namespace mongo {
// limits map fields
BSONField<long long> LimitsFields::currSize( "currSize" );
BSONField<bool> LimitsFields::hasOpsQueued( "hasOpsQueued" );
BalancerPolicy::ChunkInfo* BalancerPolicy::balance( const string& ns,
const ShardToLimitsMap& shardToLimitsMap,
const ShardToChunksMap& shardToChunksMap,
int balancedLastTime ) {
pair<string,unsigned> min("",numeric_limits<unsigned>::max());
pair<string,unsigned> max("",0);
vector<string> drainingShards;
for (ShardToChunksIter i = shardToChunksMap.begin(); i!=shardToChunksMap.end(); ++i ) {
// Find whether this shard's capacity or availability are exhausted
const string& shard = i->first;
BSONObj shardLimits;
ShardToLimitsIter it = shardToLimitsMap.find( shard );
if ( it != shardToLimitsMap.end() ) shardLimits = it->second;
const bool maxedOut = isSizeMaxed( shardLimits );
const bool draining = isDraining( shardLimits );
const bool opsQueued = hasOpsQueued( shardLimits );
// Is this shard a better chunk receiver then the current one?
// Shards that would be bad receiver candidates:
// + maxed out shards
// + draining shards
// + shards with operations queued for writeback
const unsigned size = i->second.size();
if ( ! maxedOut && ! draining && ! opsQueued ) {
if ( size < min.second ) {
min = make_pair( shard , size );
}
}
// Check whether this shard is a better chunk donor then the current one.
// Draining shards take a lower priority than overloaded shards.
if ( size > max.second ) {
max = make_pair( shard , size );
}
if ( draining && (size > 0)) {
drainingShards.push_back( shard );
}
}
// If there is no candidate chunk receiver -- they may have all been maxed out,
// draining, ... -- there's not much that the policy can do.
if ( min.second == numeric_limits<unsigned>::max() ) {
log() << "no availalable shards to take chunks" << endl;
return NULL;
}
log(1) << "collection : " << ns << endl;
log(1) << "donor : " << max.second << " chunks on " << max.first << endl;
log(1) << "receiver : " << min.second << " chunks on " << min.first << endl;
if ( ! drainingShards.empty() ) {
string drainingStr;
joinStringDelim( drainingShards, &drainingStr, ',' );
log(1) << "draining : " << ! drainingShards.empty() << "(" << drainingShards.size() << ")" << endl;
}
// Solving imbalances takes a higher priority than draining shards. Many shards can
// be draining at once but we choose only one of them to cater to per round.
const int imbalance = max.second - min.second;
const int threshold = balancedLastTime ? 2 : 8;
string from, to;
if ( imbalance >= threshold ) {
from = max.first;
to = min.first;
}
else if ( ! drainingShards.empty() ) {
from = drainingShards[ rand() % drainingShards.size() ];
to = min.first;
}
else {
// Everything is balanced here!
return NULL;
}
const vector<BSONObj>& chunksFrom = shardToChunksMap.find( from )->second;
const vector<BSONObj>& chunksTo = shardToChunksMap.find( to )->second;
BSONObj chunkToMove = pickChunk( chunksFrom , chunksTo );
log() << "chose [" << from << "] to [" << to << "] " << chunkToMove << endl;
return new ChunkInfo( ns, to, from, chunkToMove );
}
BSONObj BalancerPolicy::pickChunk( const vector<BSONObj>& from, const vector<BSONObj>& to ) {
// It is possible for a donor ('from') shard to have less chunks than a recevier one ('to')
// if the donor is in draining mode.
if ( to.size() == 0 )
return from[0];
if ( from[0]["min"].Obj().woCompare( to[to.size()-1]["max"].Obj() , BSONObj() , false ) == 0 )
return from[0];
if ( from[from.size()-1]["max"].Obj().woCompare( to[0]["min"].Obj() , BSONObj() , false ) == 0 )
return from[from.size()-1];
return from[0];
}
bool BalancerPolicy::isSizeMaxed( BSONObj limits ) {
// If there's no limit information for the shard, assume it can be a chunk receiver
// (i.e., there's not bound on space utilization)
if ( limits.isEmpty() ) {
return false;
}
long long maxUsage = limits[ ShardFields::maxSize.name() ].Long();
if ( maxUsage == 0 ) {
return false;
}
long long currUsage = limits[ LimitsFields::currSize.name() ].Long();
if ( currUsage < maxUsage ) {
return false;
}
return true;
}
bool BalancerPolicy::isDraining( BSONObj limits ) {
BSONElement draining = limits[ ShardFields::draining.name() ];
if ( draining.eoo() || ! draining.Bool() ) {
return false;
}
return true;
}
bool BalancerPolicy::hasOpsQueued( BSONObj limits ) {
BSONElement opsQueued = limits[ LimitsFields::hasOpsQueued.name() ];
if ( opsQueued.eoo() || ! opsQueued.Bool() ) {
return false;
}
return true;
}
} // namespace mongo
|
