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Re: Stopgap solution for table-size-estimate updatingproblem

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Zeugswetter Andreas DAZ SD" <ZeugswetterA(at)spardat(dot)at>
Cc: "Simon Riggs" <simon(at)2ndquadrant(dot)com>,pgsql-hackers(at)postgreSQL(dot)org
Subject: Re: Stopgap solution for table-size-estimate updatingproblem
Date: 2004-11-29 16:34:38
Message-ID: 19138.1101746078@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
"Zeugswetter Andreas DAZ SD" <ZeugswetterA(at)spardat(dot)at> writes:
> I think I recall that lseek may have a negative effect on some OS's
> readahead calculations (probably only systems that cannot handle an
> lseek to the next page eighter) ? Do you think we should cache the
> last value to avoid the syscall ?

We really can't, since the point of doing it is to find out whether any
other backends have extended the file since we last looked.  Also, IIRC
seqscan startup does a similar lseek() anyhow, so having the planner do
one will make no difference to the readahead or lack of it in a
subsequent seqscan.

			regards, tom lane

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Subject: Re: bug fix request
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