| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
| Cc: | Robert Treat <xzilla(at)users(dot)sourceforge(dot)net>, pgsql-general(at)postgresql(dot)org, Erik Jones <erik(at)myemma(dot)com> |
| Subject: | Re: Moving pgstat.stat and pgstat.tmp |
| Date: | 2007-12-05 14:39:29 |
| Message-ID: | 20951.1196865569@sss.pgh.pa.us |
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| Lists: | pgsql-general |
Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> writes:
> But then I thought, why do we need it to be a file
> at all? Why not use a mmap'ed memory area or something like that, and
> only write it to a file on postmaster shutdown?
Yeah, we definitely need some other technology for this. The difficulty
is in dealing with a highly variably sized chunk of data --- our
existing shmem approach won't work well, and once you get away from that
the old portability question raises its head.
There's also a synchronization issue: how can the stats collector make
updates appear atomic? mmap by itself doesn't solve that AFAIK.
regards, tom lane
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