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Re: Cost of XLogInsert CRC calculations

From: Greg Stark <gsstark(at)mit(dot)edu>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Cost of XLogInsert CRC calculations
Date: 2005-06-01 18:56:22
Message-ID: 87ekblucrt.fsf@stark.xeocode.com (view raw or flat)
Thread:
Lists: pgsql-hackers
It occurs to me that at least on some OSes the WAL logs are being synced with
O_SYNC or its ilk. In those cases the writes should be guaranteed to be
written out in the order postgres wrote them. So if the tail end of the WAL
entry is there (is there any sort of footer?) then the entire entry must be
there. In that case is there any need to calculate the CRC at all?

I suppose it's a bit of a problem in that the database doing the replay might
not know which sync method was used to write the entries. The format would
have to stay the same. Some magic value would have to be defined to always be
correct.

-- 
greg


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