Re: ALTER TABLE uses a bistate but not for toast tables

On Wed, Sep 07, 2022 at 10:48:39AM +0200, Drouvot, Bertrand wrote:
> Hi,
> 
> On 6/22/22 4:38 PM, Justin Pryzby wrote:
> > ATRewriteTable() calls table_tuple_insert() with a bistate, to avoid clobbering
> > and polluting the buffers.
> > 
> > But heap_insert() then calls
> > heap_prepare_insert() >
> > heap_toast_insert_or_update >
> > toast_tuple_externalize >
> > toast_save_datum >
> > heap_insert(toastrel, toasttup, mycid, options, NULL /* without bistate:( */);
> 
> What do you think about creating earlier a new dedicated bistate for the
> toast table?

Yes, but I needed to think about what data structure to put it in...

Here, I created a 2nd bistate for toast whenever creating a bistate for
heap.  That avoids the need to add arguments to tableam's
table_tuple_insert(), in addition to the 6 other functions in the call
stack.

I also updated rewriteheap.c to handle the same problem in CLUSTER:

postgres=# DROP TABLE t; CREATE TABLE t AS SELECT i, repeat((5555555+i)::text, 123456)t FROM generate_series(1,9999)i;
postgres=# VACUUM FULL VERBOSE t ; SELECT COUNT(1), datname, coalesce(c.relname,b.relfilenode::text), d.relname FROM pg_buffercache b LEFT JOIN pg_class c ON b.relfilenode=pg_relation_filenode(c.oid) LEFT JOIN pg_class d ON d.reltoastrelid=c.oid LEFT JOIN pg_database db ON db.oid=b.reldatabase GROUP BY 2,3,4 ORDER BY 1 DESC LIMIT 22;

Unpatched:
  5000 | postgres | pg_toast_96188840       | t
  => 40MB of shared buffers

Patched:
  2048 | postgres | pg_toast_17097      | t

Note that a similar problem seems to exist in COPY ... but I can't see
how to fix that one.

-- 
Justin