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Date: Wed, 6 Mar 2024 11:59:43 +0100
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Subject: Re: FSM Corruption (was: Could not read block at end of the relation)
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To: Ronan Dunklau <ronan.dunklau@aiven.io>, Noah Misch <noah@leadboat.com>,
 Michael Paquier <michael@paquier.xyz>
Cc: pgsql-bugs <pgsql-bugs@lists.postgresql.org>
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From: =?UTF-8?Q?Patrick_St=c3=a4hlin?= <patrick.staehlin@aiven.io>
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On 3/6/24 10:31, Ronan Dunklau wrote:
> Le mardi 5 mars 2024, 00:05:03 CET Noah Misch a écrit :
>> I would guess this one is more risky from a performance perspective, since
>> we'd be adding to a hotter path under RelationGetBufferForTuple().  Still,
>> it's likely fine.
> 
> I ended up implementing this in the attached patch. The idea is that we detect
> if the FSM returns a page past the end of the relation, and ignore it.
> In that case we will fallback through the extension mechanism.

@@ -582,7 +583,17 @@ RelationGetBufferForTuple(Relation relation, Size len,
  		 * We have no cached target page, so ask the FSM for an initial
  		 * target.
  		 */
+		nblocks = RelationGetNumberOfBlocks(relation);
  		targetBlock = GetPageWithFreeSpace(relation, targetFreeSpace);

I'd move the fetching of nblocks to after getting the targetBlock. This 
avoids extending the relation in the unlikely event of a FSM/relation 
extension in-between those two calls.

Patrick