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help / color / mirror / Atom feedFrom: Justin Pryzby <[email protected]>
To: Drouvot, Bertrand <[email protected]>
Cc: [email protected]
Cc: Michael Paquier <[email protected]>
Subject: Re: ALTER TABLE uses a bistate but not for toast tables
Date: Sun, 27 Nov 2022 14:15:12 -0600
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
<[email protected]>
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
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Subject: Re: ALTER TABLE uses a bistate but not for toast tables
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