Details
Major - P3 Description
Issue Status as of Oct 01, 2018
ISSUE DESCRIPTION AND IMPACT
This ticket fixes some previously redundant accounting on operation times related to sub-operations (operations triggered by another operation rather than a user command):
- Before this change, lock statistics were not re-set when starting new sub-operations, causing each sub-operation to report the aggregate lock time/lock count of itself and all preceding operations.
- After this change, each sub-operation will only report its own lock statistics in both log and currentOp() output.
To illustrate the change, below are the before and after log snippets for an aggregation operation using $out blocked by a fsyncLock for 2 seconds (for illustration purposes). Before this change:
2018-09-10T10:27:22.344-0400 I COMMAND [conn2] command test.tmp.agg_out.1 appName: "MongoDB Shell" command: create { create: "tmp.agg_out.1", temp: true, $db: "test" } numYields:0 reslen:38 locks:{ Global: { acquireCount: { r: 7, w: 1 }, acquireWaitCount: { w: 1 }, timeAcquiringMicros: { w: 2211786 } }, Database: { acquireCount: { r: 5, W: 1 } }, Collection: { acquireCount: { r: 4 } } } protocol:op_msg 2230ms
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2018-09-10T10:27:22.344-0400 I COMMAND [conn2] command test.system.indexes appName: "MongoDB Shell" command: insert { insert: "system.indexes", ordered: true, $db: "test" } ninserted:0 numYields:0 locks:{ Global: { acquireCount: { r: 8, w: 2 }, acquireWaitCount: { w: 1 }, timeAcquiringMicros: { w: 2211786 } }, Database: { acquireCount: { r: 5, W: 2 } }, Collection: { acquireCount: { r: 4 } } } protocol:op_msg 0ms
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2018-09-10T10:27:22.344-0400 I COMMAND [conn2] command admin.$cmd appName: "MongoDB Shell" command: getLastError { getlasterror: 1, $db: "admin" } numYields:0 reslen:95 locks:{ Global: { acquireCount: { r: 8, w: 2 }, acquireWaitCount: { w: 1 }, timeAcquiringMicros: { w: 2211786 } }, Database: { acquireCount: { r: 5, W: 2 } }, Collection: { acquireCount: { r: 4 } } } protocol:op_msg 0ms
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2018-09-10T10:27:22.345-0400 I COMMAND [conn2] command test.tmp.agg_out.1 appName: "MongoDB Shell" command: insert { insert: "tmp.agg_out.1", ordered: true, $db: "test" } ninserted:1 keysInserted:1 numYields:0 locks:{ Global: { acquireCount: { r: 11, w: 3 }, acquireWaitCount: { w: 1 }, timeAcquiringMicros: { w: 2211786 } }, Database: { acquireCount: { r: 7, w: 1, W: 2 } }, Collection: { acquireCount: { r: 6, w: 1 } } } protocol:op_msg 0ms
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2018-09-10T10:27:22.345-0400 I COMMAND [conn2] command admin.$cmd appName: "MongoDB Shell" command: getLastError { getlasterror: 1, $db: "admin" } numYields:0 reslen:95 locks:{ Global: { acquireCount: { r: 11, w: 3 }, acquireWaitCount: { w: 1 }, timeAcquiringMicros: { w: 2211786 } }, Database: { acquireCount: { r: 7, w: 1, W: 2 } }, Collection: { acquireCount: { r: 6, w: 1 } } } protocol:op_msg 0ms
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2018-09-10T10:27:22.345-0400 I COMMAND [conn2] command test.$cmd appName: "MongoDB Shell" command: listCollections { listCollections: 1, filter: { name: " favorite" }, cursor: {}, $readPreference: { mode: "secondaryPreferred" }, $db: "test" } numYields:0 reslen:302 locks:{ Global: { acquireCount: { r: 14, w: 3, W: 1 }, acquireWaitCount: { w: 1 }, timeAcquiringMicros: { w: 2211786 } }, Database: { acquireCount: { r: 8, w: 1, W: 2 } }, Collection: { acquireCount: { r: 7, w: 1 } } } protocol:op_msg 0ms
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2018-09-10T10:27:22.345-0400 I COMMAND [conn2] command test.favorite appName: "MongoDB Shell" command: listIndexes { listIndexes: "favorite", cursor: {}, $db: "test" } numYields:0 reslen:190 locks:{ Global: { acquireCount: { r: 15, w: 3, W: 1 }, acquireWaitCount: { w: 1 }, timeAcquiringMicros: { w: 2211786 } }, Database: { acquireCount: { r: 9, w: 1, W: 2 } }, Collection: { acquireCount: { r: 8, w: 1 } } } protocol:op_msg 0ms
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2018-09-10T10:27:22.345-0400 I COMMAND [conn2] renameCollectionForCommand: rename test.tmp.agg_out.1 to test.favorite and drop test.favorite.
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2018-09-10T10:27:22.345-0400 I STORAGE [conn2] Finishing collection drop for test.favorite (0cc548b7-6bfb-4f56-be1f-80d73b3663e0).
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2018-09-10T10:27:22.345-0400 I STORAGE [conn2] renameCollection: renaming collection 25304fc9-3257-49f6-bb9f-5b43d1884850 from test.tmp.agg_out.1 to test.favorite
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2018-09-10T10:27:22.362-0400 I COMMAND [conn2] command test.tmp.agg_out.1 appName: "MongoDB Shell" command: renameCollection { renameCollection: "test.tmp.agg_out.1", to: "test.favorite", dropTarget: true, $db: "admin" } numYields:0 reslen:38 locks:{ Global: { acquireCount: { r: 16, w: 4, W: 1 }, acquireWaitCount: { w: 1 }, timeAcquiringMicros: { w: 2211786 } }, Database: { acquireCount: { r: 9, w: 1, W: 3 } }, Collection: { acquireCount: { r: 8, w: 1 } } } protocol:op_msg 16ms
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2018-09-10T10:27:22.362-0400 I COMMAND [conn2] command test.favorite appName: "MongoDB Shell" command: aggregate { aggregate: "books", pipeline: [ { $match: { title: "1984" } }, { $out: "favorite" } ], cursor: {}, lsid: { id: UUID("0956a2cb-cfd4-4438-8842-a9c58ae0afe7") }, $db: "test" } planSummary: COLLSCAN keysExamined:0 docsExamined:3 cursorExhausted:1 numYields:1 nreturned:0 reslen:99 locks:{ Global: { acquireCount: { r: 16, w: 4, W: 1 }, acquireWaitCount: { w: 1 }, timeAcquiringMicros: { w: 2211786 } }, Database: { acquireCount: { r: 9, w: 1, W: 3 } }, Collection: { acquireCount: { r: 8, w: 1 } } } protocol:op_msg 2250ms
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After this change, note that each sub-operation does not report the
timeAcquiringMicros: {w: 2213296}
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2018-09-07T21:06:43.061-0400 I COMMAND [conn2] command test.tmp.agg_out.2 appName: "MongoDB Shell" command: create { create: "tmp.agg_out.2", temp: true,$db: "test" } numYields:0 reslen:38 locks:{ Global: { acquireCount: { r: 1, w: 1 }, acquireWaitCount: { w: 1 }, timeAcquiringMicros: { w: 2213296 } }, Database: { acquireCount: { W: 1 } } } protocol:op_msg 2232ms
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2018-09-07T21:06:43.062-0400 I COMMAND [conn2] command test.tmp.agg_out.2 appName: "MongoDB Shell" command: createIndexes { createIndexes: "tmp.agg_out.2", indexes: [ { v: 2, key: { _id: 1 }, name: "_id_", ns: "test.tmp.agg_out.2" } ], $db: "test" } numYields:0 reslen:150 locks:{ Global: { acquireCount: { r: 3, w: 1 } }, Database: { acquireCount: { r: 1, W: 1 } } } protocol:op_msg 0ms
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2018-09-07T21:06:43.064-0400 I COMMAND [conn2] command test.$cmd appName: "MongoDB Shell" command: listCollections { listCollections: 1, filter: { name: "favorite" }, cursor: {}, $readPreference: { mode: "secondaryPreferred" }, $db: "test" } numYields:0 reslen:302 locks:{ Global: { acquireCount: { r: 2 } }, Database: { acquireCount: { r: 1 } }, Collection: { acquireCount: { r: 1 } }} protocol:op_msg 0ms
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2018-09-07T21:06:43.064-0400 I COMMAND [conn2] command test.favorite appName: "MongoDB Shell" command: listIndexes { listIndexes: "favorite", cursor: {},$db: "test" } numYields:0 reslen:190 locks:{ Global: { acquireCount: { r: 1 } }, Database: { acquireCount: { r: 1 } }, Collection: { acquireCount: { r: 1 } } } protocol:op_msg 0ms
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2018-09-07T21:06:43.065-0400 I COMMAND [conn2] renameCollectionForCommand: rename test.tmp.agg_out.2 to test.favorite and drop test.favorite.
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2018-09-07T21:06:43.065-0400 I STORAGE [conn2] Finishing collection drop for test.favorite (068270d6-084f-4fb3-aa3d-b091d53109e2).
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2018-09-07T21:06:43.066-0400 I STORAGE [conn2] renameCollection: renaming collection fca8ced0-fb60-4ca1-a74f-b58001db3c88 from test.tmp.agg_out.2 to test.favorite
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2018-09-07T21:06:43.073-0400 I COMMAND [conn2] command test.tmp.agg_out.2 appName: "MongoDB Shell" command: renameCollection { renameCollection: "test.tmp.agg_out.2", to: "test.favorite", dropTarget: true, $db: "admin" } numYields:0 reslen:38 locks:{ Global: { acquireCount: { r: 1, w: 1 } }, Database: { acquireCount: { W: 1 } } } protocol:op_msg 8ms
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2018-09-07T21:06:43.073-0400 I COMMAND [conn2] CMD: drop test.tmp.agg_out.2
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2018-09-07T21:06:43.074-0400 I COMMAND [conn2] command test.$cmd appName: "MongoDB Shell" command: drop { drop: "tmp.agg_out.2", writeConcern: { w: 0, wtimeout: 0 }, $db: "test" } numYields:0 ok:0 errMsg:"ns not found" errName:NamespaceNotFound errCode:26 reslen:105 locks:{ Global: { acquireCount: { r: 1, w: 1 } }, Database: { acquireCount: { W: 1 } } } protocol:op_msg 0ms
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2018-09-07T21:06:43.074-0400 I COMMAND [conn2] command test.tmp.agg_out.2 appName: "MongoDB Shell" command: aggregate { aggregate: "books", pipeline: [ {$match: { title: "1984" } }, { $out: "favorite" } ], cursor: {}, lsid: { id: UUID("6da968ae-a6ae-445d-b11e-265eb2d31cb8") }, $db: "test" } planSummary: COLLSCAN keysExamined:0 docsExamined:3 ninserted:1 cursorExhausted:1 keysInser$ed:1 numYields:1 nreturned:0 queryHash:6E0D6672 reslen:99 locks:{ Global: { acquireCount: { r: 19, w: 5, W: 1 }, acquireWaitCount: { w: 1 }, timeAcquiringMicros: { w: 2213296 } }, Database: { acquireCount: { r: 10, w: 1, W: 4 } },Collection: { acquireCount: { r: 8, w: 1 } } } protocol:op_msg 2248ms
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AFFECTED VERSIONS
This change is available in MongoDB 4.2.
Original description
Because we don't reset LockStats when starting new sub-operations, each sub-operation will report the aggregate time of itself and all preceding operations, as well as any locking time incurred by profiling. This means the timeAcquiringMicros can quickly exceed elapsed time for the sub-operation and lead to confusion, especially as the log messages do not even indicate that the operation is a sub-operation.