mirrors/postgres
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Fix off-by-one possibly leading to skipped XLOG_RUNNING_XACTS records.

Browse Source 
Since 6ef2eba3f57f1 ("Skip checkpoints, archiving on idle systems."),
GetLastImportantRecPtr() is used to avoid performing superfluous
checkpoints, xlog switches, running-xact records when the system is
idle.  Unfortunately the check concerning running-xact records had a
off-by-one error, leading to such records being potentially skipped
when only a single record has been inserted since the last
running-xact record.

An alternative approach would have been to change
GetLastImportantRecPtr()'s definition to point to the end of records,
but that would make the checkpoint code more complicated.

Author: Andres Freund
Discussion: https://postgr.es/m/20170505012447.wsrympaxnfis6ojt@alap3.anarazel.de
Backpatch: no, code only present in master
This commit is contained in:
Andres Freund 2017-05-06 16:47:40 -07:00
parent 334b82cd56
commit e6c44eef55
2 changed files with 7 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
src/backend/postmaster/bgwriter.c
View File

@ -325,10 +325,13 @@ BackgroundWriterMain(void)
/* /*
* Only log if enough time has passed and interesting records have * Only log if enough time has passed and interesting records have
* been inserted since the last snapshot. * been inserted since the last snapshot. Have to compare with <=
* instead of < because GetLastImportantRecPtr() points at the
* start of a record, whereas last_snapshot_lsn points just past
* the end of the record.
*/ */
if (now >= timeout && if (now >= timeout &&
last_snapshot_lsn < GetLastImportantRecPtr()) last_snapshot_lsn <= GetLastImportantRecPtr())
{ {
last_snapshot_lsn = LogStandbySnapshot(); last_snapshot_lsn = LogStandbySnapshot();
last_snapshot_ts = now; last_snapshot_ts = now;

3
src/backend/postmaster/checkpointer.c
View File

@ -611,7 +611,8 @@ CheckArchiveTimeout(void)
{ {
/* /*
* Switch segment only when "important" WAL has been logged since the * Switch segment only when "important" WAL has been logged since the
* last segment switch. * last segment switch (last_switch_lsn points to end of segment
* switch occurred in).
*/ */
if (GetLastImportantRecPtr() > last_switch_lsn) if (GetLastImportantRecPtr() > last_switch_lsn)
{ {