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Re: Re: xReader, double-effort (was: Temporary tables under hot standby)

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: <simon(at)2ndquadrant(dot)com>
Cc: <andres(at)2ndquadrant(dot)com>,<aakash(dot)bits(at)gmail(dot)com>, <josh(at)postgresql(dot)org>, <pgsql-hackers(at)postgresql(dot)org>, <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Subject: Re: Re: xReader, double-effort (was: Temporary tables under hot standby)
Date: 2012-04-29 18:36:27
Message-ID: 4F9D43DB020000250004755D@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-hackers
Simon Riggs  wrote:
 
> Though it isn't a given that logical change records (LCRs) will
> require more bandwidth than physical WAL.
 
It would help if you could share a little more of what you have in
mind.  It's not yet clear to me whether you're talking about adding
logical records to the WAL stream, replacing page-oriented records in
the WAL stream with logical records, or leaving the WAL stream alone
and generating a second, new stream of logical data.
 
> WAL contains full page images, index changes and other information
> that would be absent from the LCR stream.
 
Other than full page images, which could be eliminated in other ways
before streaming the WAL, what is in the WAL file that would not be
needed to maintain an exact replica of the cluster, suitable for
quick deployment in place of a lost cluster for disaster recovery? Or
do you foresee eliminating some of the current page-image oriented
WAL records in favor of logical WAL records, with an expectation that
the logical records will be smaller?
 
> measurements and detailed analysis is required to justify how to
> proceed. Which is what is in progress now.
 
Could you clarify?  Are you referring to this discussion or some
effort at 2Q that hasn't yet been shared with the community?
 
-Kevin

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