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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>
Cc: Noah Misch <noah@leadboat.com>
Cc: Amit Khandekar <amitdkhan.pg@gmail.com>
Cc: Alvaro Herrera from 2ndQuadrant <alvherre@alvh.no-ip.org>
Cc: Andres Freund <andres@anarazel.de>
Cc: Juan José Santamaría Flecha <juanjo.santamaria@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Thomas Munro <thomas.munro@gmail.com>
Subject: Re: logical decoding : exceeded maxAllocatedDescs for .spill files
Date: Sat, 11 Jan 2020 23:20:56 -0500
Message-ID: <7490.1578802856@sss.pgh.pa.us> (raw)
In-Reply-To: <20200112041008.gddmpqunowlklc24@development>
References: <CAJ3gD9dFYJnOxUsR3MeJ=3hJKZk5XqAx-6fYUNXt6jJOK3QFMQ@mail.gmail.com>
	<20200104185148.GA2270238@rfd.leadboat.com>
	<CAJ3gD9diTB8rqyUWo=jZrSQxvW7o-gGaO6uoF5racneH3+FYOg@mail.gmail.com>
	<20200109053704.GA2502006@rfd.leadboat.com>
	<22498.1578548741@sss.pgh.pa.us>
	<CAA4eK1JitJgbOv-ie3VCXW5A74j-v0b8S55YMunwmkFDZ_4NCg@mail.gmail.com>
	<14739.1578613901@sss.pgh.pa.us>
	<18117.1578616812@sss.pgh.pa.us>
	<20200112033930.6cy3n6ybft6pp7gw@development>
	<29690.1578801237@sss.pgh.pa.us>
	<20200112041008.gddmpqunowlklc24@development>

Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
> On Sat, Jan 11, 2020 at 10:53:57PM -0500, Tom Lane wrote:
>> remind me where the win came from, exactly?

> Well, the problem is that in 10 we allocate tuple data in the main
> memory ReorderBuffer context, and when the transaction gets decoded we
> pfree() it. But in AllocSet that only moves the data to the freelists,
> it does not release it entirely. So with the right allocation pattern
> (sufficiently diverse chunk sizes) this can easily result in allocation
> of large amount of memory that is never released.

> I don't know if this is what's happening in this particular test, but I
> wouldn't be surprised by it.

Nah, don't think I believe that: the test inserts a bunch of tuples,
but they look like they will all be *exactly* the same size.

CREATE TABLE decoding_test(x integer, y text);
...

    FOR i IN 1..10 LOOP
        BEGIN
            INSERT INTO decoding_test(x) SELECT generate_series(1,5000);
        EXCEPTION
            when division_by_zero then perform 'dummy';
        END;

			regards, tom lane





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  To: pgsql-hackers@postgresql.org
  Cc: tgl@sss.pgh.pa.us, tomas.vondra@2ndquadrant.com, amit.kapila16@gmail.com, noah@leadboat.com, amitdkhan.pg@gmail.com, alvherre@alvh.no-ip.org, andres@anarazel.de, juanjo.santamaria@gmail.com, pgsql-hackers@lists.postgresql.org, robertmhaas@gmail.com, thomas.munro@gmail.com
  Subject: Re: logical decoding : exceeded maxAllocatedDescs for .spill files
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