Re: REINDEX INDEX results in a crash for an index of pg_class since 9.6

On 2019-05-01 10:06:03 -0700, Andres Freund wrote:
> I'm not sure this is the right short-term answer. Why isn't it, for now,
> sufficient to do what I suggested with RelationSetNewRelfilenode() not
> doing the CommandCounterIncrement(), and reindex_index() then doing the
> SetReindexProcessing() before a CommandCounterIncrement()? That's like
> ~10 line code change, and a few more with comments.
>
> There is the danger that the current and above approach basically relies
> on there not to be any non-inplace updates during reindex. But at the
> moment code does take care to use inplace updates
> (cf. index_update_stats()).
>
> It's not clear to me whether the approach of using
> RelationSetIndexList() in reindex_index() would be meaningfully more
> robust against non-inplace updates during reindex either - ISTM we'd
> just as well skip the necessary index insertions if we hid the index
> being rebuilt. Skipping to-be-rebuilt indexes works for
> reindex_relation() because they're going to be rebuilt subsequently (and
> thus the missing index rows don't matter) - but it'd not work for
> reindexing a single index, because it'll not get the result at a later
> stage.

FWIW, the dirty-hack version (attached) of the CommandCounterIncrement()
approach fixes the issue for a REINDEX pg_class_oid_index; in solation
even when using CCA. Started a whole CCA testrun with it, but the
results of that will obviously not be in quick.

Greetings,

Andres Freund