We are using WiredTiger on 3.0.8 version of MongoDB. The server in question is a SECONDARY which has been setup to support our read-only/query clients.
We have observed that after a heavy activity of inserts into MASTER (which are then replicated to the SECONDARY), the queries which used to run fairly fast become unusable with response times of over a minute.
Here is an example of inconsistencies that we are seeing. The problem has already occurred and performance of queries has degraded.
The following query runs fairly fast:
db.getCollection('events-qos-loadstart').count({"vd.ple.vd.pid": "57de9139-cc7e-4b5c-51fd-aaa8517028f0","vd.ple.vd.acc": "EY"}) Jan 11 18:25:28 ec2-52-23-180-212 mongod.27000[29049]: [conn11450] command cdc.$cmd command: count { count: "events-qos-loadstart", query: { vd.ple.vd.pid: "57de9139-cc7e-4b5c-51fd-aaa8517028f0", vd.ple.vd.acc: "EY" }, fields: {} } planSummary: COUNT_SCAN { vd.ple.vd.acc: 1, vd.ple.vd.pid: 1, vd.pec: 1, vd.ts: 1 } keyUpdates:0 writeConflicts:0 numYields:1817 reslen:44 locks:{ Global: { acquireCount: { r: 3636 }, acquireWaitCount: { r: 37 }, timeAcquiringMicros: { r: 134261 } }, Database: { acquireCount: { r: 1818 } }, Collection: { acquireCount: { r: 1818 } } } 218ms Count: 232691
A similar query with just additional parameter is taking an incredibly longer time to run:
db.getCollection('events-qos-loadstart').count({"vd.ple.vd.pid": "57de9139-cc7e-4b5c-51fd-aaa8517028f0","vd.ple.vd.acc": "EY", "vd.pec": {"$gte": 2}}) Jan 11 18:32:33 ec2-52-23-180-212 mongod.27000[29049]: [conn11450] command cdc.$cmd command: count { count: "events-qos-loadstart", query: { vd.ple.vd.pid: "57de9139-cc7e-4b5c-51fd-aaa8517028f0", vd.ple.vd.acc: "EY", vd.pec: { $gte: 2.0 } }, fields: {} } planSummary: IXSCAN { vd.ple.vd.acc: 1, vd.ple.vd.pid: 1, vd.pec: 1, vd.ts: 1 } keyUpdates:0 writeConflicts:0 numYields:3444 reslen:44 locks:{ Global: { acquireCount: { r: 6890 }, acquireWaitCount: { r: 2074 }, timeAcquiringMicros: { r: 29318135 } }, Database: { acquireCount: { r: 3445 } }, Collection: { acquireCount: { r: 3445 } } } 85835ms Count: 231445
Here are the indexes which are defined on this collection:
[
{
"v" : 1,
"key" : {
"_id" : 1
},
"name" : "_id_",
"ns" : "cdc.events-qos-loadstart"
},
{
"v" : 1,
"key" : {
"vd.ple.vd.acc" : 1,
"vd.ts" : 1,
"vd.pec" : 1
},
"name" : "vd.ple.vd.acc_1_vd.ts_1_vd.pec_1",
"ns" : "cdc.events-qos-loadstart"
},
{
"v" : 1,
"key" : {
"vd.ts" : 1,
"vd.pec" : 1
},
"name" : "vd.ts_1_vd.pec_1",
"ns" : "cdc.events-qos-loadstart"
},
{
"v" : 1,
"key" : {
"vd.ple.vd.acc" : 1,
"vd.ple.vd.pid" : 1,
"vd.pec" : 1,
"vd.ts" : 1
},
"name" : "vd.ple.vd.acc_1_vd.ple.vd.pid_1_vd.pec_1_vd.ts_1",
"ns" : "cdc.events-qos-loadstart"
}
]
Note that all the fields are in an index.
If I restart the server, both of these queries will return in milliseconds.
- is duplicated by
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SERVER-29931 Query plan is different for '$gte' and '$gt'
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- Closed
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- Closed
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- related to
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- Closed
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