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Re: Stopgap solution for table-size-estimate updatingproblem

From: "Zeugswetter Andreas DAZ SD" <ZeugswetterA(at)spardat(dot)at>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Simon Riggs" <simon(at)2ndquadrant(dot)com>,<pgsql-hackers(at)postgreSQL(dot)org>
Subject: Re: Stopgap solution for table-size-estimate updatingproblem
Date: 2004-11-30 10:57:34
Message-ID: 46C15C39FEB2C44BA555E356FBCD6FA40184D251@m0114.s-mxs.net (view raw or flat)
Thread:
Lists: pgsql-hackers
>> 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

Well yes. The value would need to be kept ajour by the backends that 
extend, with an interlocked increment. We would thus need to keep the 
count in shmem.

Andreas

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