[SERVER-23272] Remove misleading/not useful diagnostic metrics Created: 21/Mar/16  Updated: 17/May/19  Resolved: 27/Apr/16

Status: Closed
Project: Core Server
Component/s: Diagnostics, Querying
Affects Version/s: None
Fix Version/s: 3.3.6

Type: Improvement Priority: Major - P3
Reporter: James Wahlin Assignee: James Wahlin
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Depends
depends on SERVER-23259 Report planSummary in per-operation d... Closed
depends on SERVER-23271 Add metrics to track index key additi... Closed
Related
is related to SERVER-7897 keyUpdates not updated on array/multi... Closed
is related to SERVER-23635 The 'keyUpdates' metric only reflects... Closed
is related to SERVER-23081 keyUpdates not set on MMAPv1 document... Closed
is related to DOCS-7697 Deprecate 'fastmodinsert' metric for ... Closed
is related to DOCS-7761 MongoDB 3.4: Remove keyUpdates, fastm... Closed
is related to SERVER-23831 Remove the 'fastmodinsert' metric Closed
is related to SERVER-23861 Add keysInserted & keysDeleted to ser... Backlog
Backwards Compatibility: Major Change
Sprint: Query 13 (04/22/16), Query 14 (05/13/16)
Participants:

 Description   
  • keyUpdates: This metric tracks the # of index entries added on the update path. It does not track index changes due to upsert, removal of index entries or for write operations other than update. It also is not tracked for updates that cause document move (SERVER-23081). A feature request (SERVER-23271) has been filed to add more comprehensive metrics, covering all write operations/commands for each of insert/update/delete.
  • fastmod: Tracks update operations under MMAPv1 that: a) Do not cause update of index keys. b) Are non-destructive updates. c) Do not result in document move (which we also track via the 'nmoved' metric). This behavior is hard to understand and of limited use when troubleshooting operation performance.
  • fastmodinsert: Tracks update operations that result in an insert, given the update is structured as a document replacement, rather than modification. This metric has not been considered useful in troubleshooting operation performance.
  • idhack: Use of idhack is reported in the planSummary. There is no need to track independently, once planSummary is universally reported under SERVER-23259.
  • moved: Boolean value indicating whether an MMAPv1 document has moved on disk. This metric has been obsolete since the introduction of nmoved, whose presence and value of 1 or more indicates 'moved'.


 Comments   
Comment by Githook User [ 27/Apr/16 ]

Author:

{u'username': u'jameswahlin', u'name': u'James Wahlin', u'email': u'james.wahlin@10gen.com'}

Message: SERVER-23272 Remove idhack metric
Branch: master
https://github.com/mongodb/mongo/commit/c0822ee332921f77d9a3466d23cf3f75ab80cf4d

Comment by Githook User [ 27/Apr/16 ]

Author:

{u'username': u'jameswahlin', u'name': u'James Wahlin', u'email': u'james.wahlin@10gen.com'}

Message: SERVER-23272 Deprecate idhack metric in SNMP
Branch: master
https://github.com/10gen/mongo-enterprise-modules/commit/d05e5a64e4a4ac30710aeb84fd315b88ea2197e2

Comment by James Wahlin [ 25/Apr/16 ]

Work remaining on this ticket:

  1. Remove idhack metric (dependent on SERVER-23259)
  2. Enter DOCS ticket to remove 'keyUpdates', 'fastmod', 'idhack' and 'moved' metrics from our documentation for 3.4.
Comment by Githook User [ 25/Apr/16 ]

Author:

{u'username': u'jameswahlin', u'name': u'James Wahlin', u'email': u'james.wahlin@10gen.com'}

Message: SERVER-23272 Remove 'keyUpdates', 'fastmod' and 'moved' metrics
Branch: master
https://github.com/mongodb/mongo/commit/85f3d108a95e4286fe03e517a586ce9f34d12d53

Comment by Githook User [ 25/Apr/16 ]

Author:

{u'username': u'jameswahlin', u'name': u'James Wahlin', u'email': u'james.wahlin@10gen.com'}

Message: SERVER-23272 Deprecate 'fastmod' metric in SNMP
Branch: master
https://github.com/10gen/mongo-enterprise-modules/commit/1a968169d725110d8174b5323327aafae217d6ce

Comment by James Wahlin [ 20/Apr/16 ]

Created SERVER-23831 to consider removal of 'fastmodinsert' post MongoDB 3.4 release and general adoption.

Comment by James Wahlin [ 20/Apr/16 ]

We are adding removal of the 'moved' metric to the scope of this ticket. 'moved' has been obsolete since the introduction of 'nmoved'.

Comment by James Wahlin [ 20/Apr/16 ]

Created DOCS-7697 to request deprecation of 'fastmodinsert' in MongoDB 3.4

Comment by James Wahlin [ 11/Apr/16 ]

As part of our work on SERVER-23271, we found a bug regarding the keyUpdates metric. We zero out this metric on call to Collection::updateDocument. This serves its purpose when updating a single document, but when performing a multi-update, only the last document updated will be reflected. SERVER-23635 entered to track.

We won't fix keyUpdates for 3.4 as we plan to remove under this ticket. Backport to 3.0 and 3.2 should be considered.

Comment by James Wahlin [ 25/Mar/16 ]

After discussion with scotthernandez & jason.rassi, our current thoughts are to:

  1. Remove keyUpdates and fastmod, with a dependency on creation of a new "keysAffected" metric (SERVER-23271)
  2. Deprecate fastmodinsert for 3.4, and enter a separate ticket for future removal. Feedback received during the deprecation period will help determine whether a) We should remove outright b) We should replace with a better metric - potentially something that is meaningful for all storage engines or c) We should leave in place as-is.
  3. Remove idhack, with a dependency on adding planSummary for all relevant operations (SERVER-23259)
Comment by Scott Hernandez (Inactive) [ 21/Mar/16 ]

Not sure about "fastmod" not being useful. Also, keyUpdates has been very useful in the past and we should not remove it until we better functionality.

While removing these might clean code up I'd be concerned that we need to replace/improve reporting first, before removing.

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