2011/10/12 Jun Ishiduka <ishizuka....@po.ntts.co.jp>:
> > ERROR: full_page_writes on master is set invalid at least once since
> > latest checkpoint
> >
> > I think this error should be rewritten as
> > ERROR: full_page_writes on master has been off at some point since
> > latest checkpoint
> >
> > We should be using 'off' instead of 'invalid' since that is what is what
> > the user sets it to.
> Sure.

What about the following message? It sounds more precise to me.

ERROR: WAL generated with full_page_writes=off was replayed since last

> I updated to patch corresponded above-comments.

Thanks for updating the patch! Here are the comments:

         * don't yet have the insert lock, forcePageWrites could change under 
         * but we'll recheck it once we have the lock.
-       doPageWrites = fullPageWrites || Insert->forcePageWrites;
+       doPageWrites = Insert->fullPageWrites || Insert->forcePageWrites;

The source comment needs to be modified.

         * just turned off, we could recompute the record without full pages, 
         * we choose not to bother.)
-       if (Insert->forcePageWrites && !doPageWrites)
+       if ((Insert->fullPageWrites || Insert->forcePageWrites) && 

Same as above.

+       LWLockAcquire(WALInsertLock, LW_EXCLUSIVE);
+       XLogCtl->Insert.fullPageWrites = fullPageWrites;
+       LWLockRelease(WALInsertLock);

I don't think WALInsertLock needs to be hold here because there is no
concurrently running process which can access Insert.fullPageWrites.
For example, Insert->currpos and Insert->LogwrtResult are also changed
without the lock there.

The source comment of XLogReportParameters() needs to be modified.

XLogReportParameters() should skip writing WAL if full_page_writes has not been
changed by SIGHUP.

XLogReportParameters() should skip updating pg_control if any parameter related
to hot standby has not been changed.

+       if (!fpw_manager)
+       {
+               LWLockAcquire(WALInsertLock, LW_EXCLUSIVE);
+               fpw = XLogCtl->Insert.fullPageWrites;
+               LWLockRelease(WALInsertLock);

It's safe to take WALInsertLock with shared mode here.

In checkpoint, XLogReportParameters() is called only when wal_level is
OTOH, in walwriter, it's always called even when wal_level is not hot_standby.
Can't we skip calling XLogReportParameters() whenever wal_level is not

In do_pg_start_backup() and do_pg_stop_backup(), the spinlock must be held to
see XLogCtl->lastFpwDisabledLSN.

+       /* check whether the master's FPW is 'off' since pg_start_backup. */
+       if (recovery_in_progress && XLByteLE(startpoint, 
+               ereport(ERROR,
+                         errmsg("full_page_writes on master has been off at 
some point
during online backup")));

What about changing the error message to:
ERROR: WAL generated with full_page_writes=off was replayed during online backup


Fujii Masao
NTT Open Source Software Center

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