Re: shared-memory based stats collector

From: Andres Freund <andres(at)anarazel(dot)de>
To: Magnus Hagander <magnus(at)hagander(dot)net>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: shared-memory based stats collector
Date: 2018-07-06 20:10:36
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On 2018-07-06 22:03:12 +0200, Magnus Hagander wrote:
> *If* we can provide the snapshots view of them without too much overhead I
> think it's worth looking into that while *also* proviiding a lower overhead
> interface for those that don't care about it.

I don't see how that's possible without adding significant amounts of
complexity and probably memory / cpu overhead. The current stats already
are quite inconsistent (often outdated, partially updated, messages
dropped when busy) - I don't see what we really gain by building
something MVCC like in the "new" stats subsystem.

> If it ends up that keeping the snapshots become too much overhead in either
> in performance or code-maintenance, then I agree can probably drop that.
> But we should at least properly investigate the cost.

I don't think it's worthwhile to more than think a bit about it. There's
fairly obvious tradeoffs in complexity here. Trying to get there seems
like a good way to make the feature too big.


Andres Freund

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