Horton

Re: Synchronous replication - patch status inquiry

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Simon Riggs <simon@2ndQuadrant.com>
Cc: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>, Dimitri Fontaine <dfontaine@hi-media.com>, Fujii Masao <masao.fujii@gmail.com>, Robert Haas <robertmhaas@gmail.com>, David Fetter <david@fetter.org>, Bruce Momjian <bruce@momjian.us>, fazool mein <fazoolmein@gmail.com>, pgsql-hackers@postgresql.org
Date: 2010-09-07T14:47:27Z
Lists: pgsql-hackers 
Simon Riggs <simon@2ndQuadrant.com> writes:
> On Tue, 2010-09-07 at 09:27 +0300, Heikki Linnakangas wrote:
>> For the sake of argument, yes that's what I was thinking. Now please 
>> explain how *you're* thinking it should work.

> The WAL is sent from master to standby in 8192 byte chunks, frequently
> including multiple commits. From standby, one reply per chunk. If we
> need to wait for apply while nothing else is received, we do. 

That premise is completely false.  SR does not send WAL in page units.
If it did, it would have the same performance problems as the old
WAL-file-at-a-time implementation, just with slightly smaller
granularity.

			regards, tom lane