#84 389 Directory Server Unnecessary Checkpoints
Closed: wontfix None Opened 9 years ago by mkosek.


Description of problem:

Even when there have been no logging activity, ns-slapd forces a checkpoint,
generating unnecessary disk traffic.

Version-Release number of selected component (if applicable):


How reproducible:


Steps to Reproduce:
1.On a quiescent system do "pidstat -C ns-slapd -d 60"

Actual results:
Disk writes are reported

Expected results:
No disk writes

Additional info:

Also "ls -lrt /var/lib/dirsrv/slapd-<server>/db" shows the log file and the __
db.nnn files regularly being updated.

This is apparently due to checkpoint being called (in
db_layer.c:dblayer_txn_checkpoint()) with the DB_FORCE option.

Is there any reason to force these checkpoints?

I am using the server for user data (uid/gid etc) but not passwords (because
I'm using kerberos for that). The ldap data hardly ever changes and I'd like to
let the disks spindown in quiet times. An option, at least, to not force
checkpoints would be nice.

batch move to milestone 1.3

Fix description: txn_checkpoint was always called with DB_FORCE flag.
This patch introduces db_force arg to dblayer_txn_checkpoint and
DB_FORCE is passed only from dblayer_force_checkpoint.

Note: checkpoint_threadmain is one of the BDB housekeeping threads.
It calls txn_checkpoint periodically. The interval is specified in
the ldbm database config:
dn: cn=config,cn=ldbm database,cn=plugins,cn=config
nsslapd-db-checkpoint-interval: <second>
Even if DB_FORCE is not set and there is no db modify activities,
as long as checkpoint thread is functioning, some disk IO is
observed due to updating the lock table and mempool to check if
there is any data to flush.

Steps to verify:
NO #84 patch>

pidstat -C ns-slapd -d 60

01:46:32 PM PID kB_rd/s kB_wr/s kB_ccwr/s Command
01:47:32 PM 26830 0.00 1.13 0.00 ns-slapd
01:48:32 PM 26830 0.00 1.07 0.00 ns-slapd
01:49:32 PM 26830 0.00 1.13 0.00 ns-slapd

With #84 patch>
$ pidstat -C ns-slapd -d 60
02:18:29 PM PID kB_rd/s kB_wr/s kB_ccwr/s Command
02:19:29 PM 1739 0.00 0.27 0.00 ns-slapd
02:20:29 PM 1739 0.00 0.27 0.00 ns-slapd
02:21:29 PM 1739 0.00 0.27 0.00 ns-slapd
Write IO is less than "NO #84 patch".

Set high value to nsslapd-db-checkpoint-interval>
$ pidstat -C ns-slapd -d 60
03:58:52 PM PID kB_rd/s kB_wr/s kB_ccwr/s Command
03:59:52 PM PID kB_rd/s kB_wr/s kB_ccwr/s Command
04:00:52 PM PID kB_rd/s kB_wr/s kB_ccwr/s Command
Unless checkpoint thread calls txn_checkpoint, there is no IO.

Reviewed by Rich (Thanks!!!)

Pushed to master.

$ git merge trac84
Updating d962cea..d419e1f
ldap/servers/slapd/back-ldbm/dblayer.c | 26 ++++++++++++--------------
1 files changed, 12 insertions(+), 14 deletions(-)

$ git push
Counting objects: 13, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (7/7), done.
Writing objects: 100% (7/7), 1.18 KiB, done.
Total 7 (delta 5), reused 0 (delta 0)
To ssh://git.fedorahosted.org/git/389/ds.git
d962cea..d419e1f master -> master

Added initial screened field value.

Metadata Update from @nhosoi:
- Issue assigned to nhosoi
- Issue set to the milestone: 1.2.11.a1

4 years ago

389-ds-base is moving from Pagure to Github. This means that new issues and pull requests
will be accepted only in 389-ds-base's github repository.

This issue has been cloned to Github and is available here:
- https://github.com/389ds/389-ds-base/issues/84

If you want to receive further updates on the issue, please navigate to the github issue
and click on subscribe button.

Thank you for understanding. We apologize for all inconvenience.

Metadata Update from @spichugi:
- Issue close_status updated to: wontfix (was: Fixed)

9 months ago

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