How to understand the mongodb execution plan
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= Mongodb concurrent batch kill session =
Concurrent, batch kill session
1. Drop all session kill with query time longer than 1000s.
Db.currentOp () .inprog.forEach (function (item) {if (item.secs_running > 1000 & & item.op = = "query") db.killOp (item.opid)})
2. Kill all jack.bear queries that contain collections
Db.currentOp () .inprog.forEach (function (item) {if (item.ns = = "jack.bear" & & item.op = = "query") db.killOp (item.opid)})
3. Kill the operations that meet the three conditions of item.op== "query" & & item.secs_running > 60 & & item.ns== "jack.bear".
Db.currentOp () .inprog.forEach (function (item) {if (item.waitingForLock) {var lock_info = item ["opid"]; if (item.op== "query" & & item.secs_running > 60 & & item.ns== "cswuyg.cswuyg") {db.killOp (item.opid)})
4. Kill the operations that meet the two conditions of item.op = = "query" & & item.secs_running > 1000
Db.currentOp () .inprog.forEach (function (item) {
Var lock_info = item ["opid"]
If (item.op = = "query" & & item.secs_running > 1000) {
Print ("kill", item.opid)
Db.killOp (item.opid)
}
})
# MongoDB execution Plan #
Stage classification
COLLSCAN: scan entire collection IXSCAN: index scan FETCH: retrieve and select document based on the index
SHARD_MERGE: merge the returned data of each shard
SORT: indicates that it is sorted in memory (consistent with the previous version of scanAndOrder:true)
LIMIT: use limit to limit the number of returns
SKIP: skip IDHACK with skip: check against _ id
SHARDING_FILTER: query sharded data through mongos
COUNT: use db.coll.explain (). Count () and the like for count
COUNTSCAN:count does not use the stage return when using Index for count
COUNT_SCAN:count returns SUBPLA from stage when using Index for count: stage return from $or query that does not use the index
TEXT: stage returns PROJECTION when querying with full-text index: limit the return of stage when fields are returned
= re-index =
Re-index:
Db.tableName.dropIndex ("indexName")
Db.tableName.ensureIndex ({"key1": 1, "key2": 1}, {"name": "indexName"}, {background:true})
Db.COLLECTION_NAME.ensureIndex ({"uuid":-1}, {background:true})
Db.COLLECTION_NAME.getIndexes ()
= = View execution plan = =
Db.collection_name.find ({}) .explain (true)
Specific query conditions should be set in find {} before the exact execution plan can be found.
When MongoDB looks at the execution plan, the ideal state is:-- 20180604
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