Date: Wed, 31 Aug 2016 16:11:38 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Pavan Deolasee <pavan.deolasee@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Patch: Write Amplification Reduction Method (WARM)
Message-ID: <20160831201138.GD31352@momjian.us>
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On Wed, Aug 31, 2016 at 04:03:29PM -0400, Bruce Momjian wrote:
> Why not just remember the tid of chains converted from WARM to HOT, then
> use "amrecheck" on an index entry matching that tid to see if the index
> matches one of the entries in the chain.  (It will match all of them or
> none of them, because they are all red.)  I don't see a point in
> coloring the index entries as reds as later you would have to convert to
> blue in the WARM-to-HOT conversion, and a vacuum crash could lead to
> inconsistencies.  Consider that you can just call "amrecheck" on the few
> chains that have converted from WARM to HOT.  I believe this is more
> crash-safe too.  However, if you have converted WARM to HOT in the heap,
> but crash during the index entry removal, you could potentially have
> duplicates in the index later, which is bad.

I think Pavan had the "crash durin the index entry removal" fixed via:

> During the second heap scan, we fix WARM chain by clearing HEAP_WARM_TUPLE flag
> and also reset Red flag to Blue.

so the marking from WARM to HOT only happens after the index has been cleaned.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I. As I am, so you will be. +
+                     Ancient Roman grave inscription +


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