I wonder why we are monitoring time of writing to WAL, but not time of
fsyncing WAL segments?
Is there are principle reason for it or just because nobody added it yet?
If so, please find very small patch which adding WAIT_EVENT_WAL_FSYNC
event type.
Our engineers in PgPro complain me that there is no information about
time spent in syncing WALs...
Unfortunately Postgres still is not able to aggregate this statistic.
But at least we have pg_wait_sampling extension for it:
https://github.com/postgrespro/pg_wait_sampling
--
Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index c2adb22..ef0addd 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -1682,6 +1682,10 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry><literal>WALWrite</literal></entry>
<entry>Waiting for a write to a WAL file.</entry>
</row>
+ <row>
+ <entry><literal>WALFsync</literal></entry>
+ <entry>Waiting for a fsync for WAL segment.</entry>
+ </row>
</tbody>
</tgroup>
</table>
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 1a419aa..0956655 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -10156,6 +10156,7 @@ assign_xlog_sync_method(int new_sync_method, void *extra)
void
issue_xlog_fsync(int fd, XLogSegNo segno)
{
+ pgstat_report_wait_start(WAIT_EVENT_WAL_FSYNC);
switch (sync_method)
{
case SYNC_METHOD_FSYNC:
@@ -10191,6 +10192,7 @@ issue_xlog_fsync(int fd, XLogSegNo segno)
elog(PANIC, "unrecognized wal_sync_method: %d", sync_method);
break;
}
+ pgstat_report_wait_end();
}
/*
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 084573e..adbf6af 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -3931,6 +3931,9 @@ pgstat_get_wait_io(WaitEventIO w)
case WAIT_EVENT_WAL_WRITE:
event_name = "WALWrite";
break;
+ case WAIT_EVENT_WAL_FSYNC:
+ event_name = "WALFsync";
+ break;
/* no default case, so that compiler will warn */
}
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index be2f592..b76074b 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -922,7 +922,8 @@ typedef enum
WAIT_EVENT_WAL_INIT_WRITE,
WAIT_EVENT_WAL_READ,
WAIT_EVENT_WAL_SYNC_METHOD_ASSIGN,
- WAIT_EVENT_WAL_WRITE
+ WAIT_EVENT_WAL_WRITE,
+ WAIT_EVENT_WAL_FSYNC
} WaitEventIO;
/* ----------
