Re: FSM Corruption (was: Could not read block at end of the relation)

Le mercredi 6 mars 2024, 11:59:43 CET Patrick Stählin a écrit :
> 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.

Good catch. Please find attached v2 of the patch. 

--
Ronan Dunklau