[SERVER-16565] FsyncLock on WT should not imply "snapshotting" is OK Created: 16/Dec/14  Updated: 27/Oct/15  Resolved: 12/Jan/15

Status: Closed
Project: Core Server
Component/s: Concurrency, Usability
Affects Version/s: None
Fix Version/s: 2.8.0-rc5

Type: Improvement Priority: Minor - P4
Reporter: Osmar Olivo Assignee: Matt Kangas
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Documented
is documented by DOCS-4652 Update fsync documentation to clarify... Closed
Related
related to SERVER-17557 Display warning when running db.fsync... Closed
is related to DOCS-4536 FSync+Lock does not work on WT Closed
Backwards Compatibility: Fully Compatible
Participants:

 Description   

When WiredTiger is the active storage engine, db.fsyncLock() does not completely quiesce the database. Writes may still occur in the background.

We should not imply that the database is locked "for snapshotting" in this state.



 Comments   
Comment by Githook User [ 12/Jan/15 ]

Author:

{u'username': u'kangas', u'name': u'Matt Kangas', u'email': u'matt.kangas@mongodb.com'}

Message: SERVER-16565 change FSyncCommand log message

Remove phrase that is misleading when storageEngine=wiredTiger
Branch: master
https://github.com/mongodb/mongo/commit/0d54e7060d151a1585505ba09fddf78efff7ff10

Comment by Daniel Pasette (Inactive) [ 12/Jan/15 ]

that is probably a good idea. feel free to re-open.

Comment by Matt Kangas [ 12/Jan/15 ]

Maybe we should remove the "for snapshotting" part of this log message.

2015-01-12T16:15:45.768-0500 I STORAGE  [conn1] db is now locked for snapshotting, no writes allowed. db.fsyncUnlock() to unlock
2015-01-12T16:15:45.768-0500 I STORAGE  [conn1]     For more info see http://dochub.mongodb.org/core/fsynccommand
2015-01-12T16:17:11.526-0500 I COMMAND  [conn1] command: unlock requested

The command returns a message that still makes sense for WT, I think.

> db.fsyncLock()
{
	"info" : "now locked against writes, use db.fsyncUnlock() to unlock",
	"seeAlso" : "http://dochub.mongodb.org/core/fsynccommand",
	"ok" : 1
}

Comment by Daniel Pasette (Inactive) [ 12/Jan/15 ]

Don't think this is necessary. The locking part works and the fsync part works. We do need to write the documentation which explains that under the hood, with WT, data may be moving.

Comment by Daniel Pasette (Inactive) [ 18/Dec/14 ]

would be good to message this in the cmd results if possible.

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