Re: Performance of COPY for Archive operations - Mailing list pgsql-hackers-win32
From | Bruce Momjian |
---|---|
Subject | Re: Performance of COPY for Archive operations |
Date | |
Msg-id | 200409202235.i8KMZmA02435@candle.pha.pa.us Whole thread Raw |
In response to | Re: Performance of COPY for Archive operations ("Simon Riggs" <simon@2ndquadrant.com>) |
Responses |
Re: Performance of COPY for Archive operations
(Bruce Momjian <pgman@candle.pha.pa.us>)
|
List | pgsql-hackers-win32 |
We already have a warning that prints when checkpoints happen too frequently. I wonder if we should print a warning if the number of WAL records doubles from its maximum which is checkpoint_segments*2+1 I think. --------------------------------------------------------------------------- Simon Riggs wrote: > >Tom Lane wrote > > "Simon Riggs" <simon@2ndquadrant.com> writes: > > > Nothing that surprising there, though I think I would like to > > put a WARNING > > > message into the Archiver that triggers if more than > > CHECKPOINT_SEGMENTS WAL > > > files are ready to archive at any one time. Though maybe that > > would cause > > > more problems than it would solve: "Archiving of transaction logs cannot > > > keep up with system activity. If this occurs regularly, you should > > > reconsider your database-disk layout" > > > > Can't see the value of this. The problem will be readily apparent from > > growth of the pg_xlog directory --- anyone who doesn't notice that > > probably isn't perusing the postmaster log either. > > Hmmm, message levels were a point we differed on previously, IIRC. > > Certainly, if the growth happened over a long period, then I'd agree - the > admin should have spotted it. > > If the behaviour were more volatile, then the admin might not spot it - the > effects are only shown when the system becomes I/O bound, which might be > regularly at peak loading, but never long enough to notice. I had considered > just such volatility in the design, though with regard to operator induced > behaviour like tape changes or deliberate batching of log files. > > The issue is that by falling behind the archiver is increasing the > transaction loss window, possibly undermining somewhat the purpose of PITR. > > The message shows in the log long after the situation occurred and the space > increase has disipated. The admin may never look at the logs, agreed, but if > the message isn't there they certainly will never notice. You and I will > know, because when the crash occurs, we'll get a pattern of error messages > we'll recognise, but thats not much help to the admin. > > Do we wait for such a crash before we add the hint? > > > Also, once it starts > > to bleat, what's going to make it stop? Filling the disk with warning > > messages won't be a constructive improvement on the situation :-( > > Filling the disk with log messages would be pointless, agreed. > > If the message appeared as part of the normal archiver cycle, then the > message would only appear once per 2*CHECKPOINT_SEGMENTS "transaction log > archived" and "transaction log recycled" messages. Thus no more likely to > fill up the disk. > > Of course, the archiver could always report less frequently, since it keeps > state between cycles. > > I'm not in a rush to add this, just think its needed, based upon my > observations on Windows. > > Best Regards, Simon Riggs > > > ---------------------------(end of broadcast)--------------------------- > TIP 9: the planner will ignore your desire to choose an index scan if your > joining column's datatypes do not match > -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
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