Re: global temporary table (GTT) - are there some ideas how to implement it?

On 12/01/2026 8:57 AM, Pavel Stehule wrote:
> Hi
>
>
> I do not completely understand how partitioning of system tables can
> solve this problem.
> Do you propose that each backend has its own (private) partition?
> It seems to be impossible and can cause even worse catalog bloating
> (instead of  one temp table we will have to create temp partitions
> for
> multiple system tables).
>
>
> yes - but what is important - each backend has its own global temp
> partitions. Then almost all metadata will be static and only statistic
> related will be temporary.
>
> The backend related partitions have to be of global temp table, not
> local temp table (only then it makes sense).
>
> The main target is removing bloat from the system catalog, and it is
> impossible without storing system data to GTT.

So do I correctly understand that at least pg_class and pg_statistics
will have two partitions: "global" and "local" and last one will act as
GTT: it has shared metadata but private data. It can work for
pg_statistics, because it is actually only needed for the particular
backend.
But it will not work for pg_class, because all backends should observe
information about this table, but each of them should see it's own
relpages/reltuples.  So we need some kind of CoW here. Not sure that
partitioning can solve this problem...

Also even if we manage to somehow solve this problem and provide private
version of pg_statistics/pg_class, it is not clear who and when will
fill this data.
Autovacuum is not processing temp tables. There was autoanalyze
extension which allows to do analyze on demand inside backend itself.
But I am not sure that it can be considered as general approach for GTT.
Alternative is to store GTT data in share buffers, rather than in local
backend memory.
It will also solve other problems with temporary tables, i.e. connection
pooling.