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This article introduces the relevant knowledge of "how to understand the mongodb implementation plan". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

= 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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