shared memory size during upgrade pgsql with partitions

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shared memory size during upgrade pgsql with partitions

Piotr Włodarczyk
Hello,

Currently we're working on PSQL 11.5 and we're trying upgrade to 12.1.

During that we have a problem:

command: "/usr/pgsql-12/bin/pg_dump" --host /cluster/postgresql --port 50432
--username postgres --schema-only --quote-all-identifiers --binary-upgrade
--format=custom  --file="pg_upgrade_dump_281535902.custom" 'dbname=sprint'
>> "pg_upgrade_dump_281535902.log" 2>&1
pg_dump: error: query failed: ERROR:  out of shared memory
HINT:  You might need to increase max_locks_per_transaction.
pg_dump: error: query was: LOCK TABLE
"some_schemaa"."table_part_80000000_2018q3" IN ACCESS SHARE MODE

On current instance we have about one thousand of partitions, partitioned in
two levels: first by id_product, and second level by quarter of the year, as
you can see on above log.

How have we to calculate shared memory, and (eventually
max_locks_per_transaction) to be fit to the limits during upgrade?

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Re: shared memory size during upgrade pgsql with partitions (max_locks_per_transaction)

Justin Pryzby
On Tue, Dec 17, 2019 at 08:03:41PM +0000, Piotr Włodarczyk wrote:

> Currently we're working on PSQL 11.5 and we're trying upgrade to 12.1.
>
> During that we have a problem:
>
> command: "/usr/pgsql-12/bin/pg_dump" --host /cluster/postgresql --port 50432
> --username postgres --schema-only --quote-all-identifiers --binary-upgrade
> --format=custom  --file="pg_upgrade_dump_281535902.custom" 'dbname=sprint'
> >> "pg_upgrade_dump_281535902.log" 2>&1
> pg_dump: error: query failed: ERROR:  out of shared memory
> HINT:  You might need to increase max_locks_per_transaction.
> pg_dump: error: query was: LOCK TABLE
> "some_schemaa"."table_part_80000000_2018q3" IN ACCESS SHARE MODE
>
> On current instance we have about one thousand of partitions, partitioned in
> two levels: first by id_product, and second level by quarter of the year, as
> you can see on above log.
>
> How have we to calculate shared memory, and (eventually
> max_locks_per_transaction) to be fit to the limits during upgrade?

Great question.  Clearly, if you can run that (or similar) pg_dump command,
then you can pg_upgrade.  I think you could also do pg_upgrade --check,

The query looks like
                FROM pg_class c...
                WHERE c.relkind in ('%c', '%c', '%c', '%c', '%c', '%c', '%c') "

..and then does:

                if (tblinfo[i].dobj.dump &&
                        (tblinfo[i].relkind == RELKIND_RELATION ||
                         tblinfo->relkind == RELKIND_PARTITIONED_TABLE) &&
                        (tblinfo[i].dobj.dump & DUMP_COMPONENTS_REQUIRING_LOCK))
                {
                        resetPQExpBuffer(query);
                        appendPQExpBuffer(query,
                                                          "LOCK TABLE %s IN ACCESS SHARE MODE",
                                                          fmtQualifiedDumpable(&tblinfo[i]));
                        ExecuteSqlStatement(fout, query->data);
                }

..then filters by -N/-n/-t/-T (which doesn't apply to pg_upgrade):
                        selectDumpableTable(&tblinfo[i], fout);

So it looks like COUNT(1) FROM pg_class WHERE relkind IN ('r','p') should do it.

But actually, during pg_upgrade, since nothing else is running, you actually
have max_connections*max_locks_per_transaction total locks.

Said differently, I think you could set max_locks_per_transaction to:
SELECT (SELECT COUNT(1) FROM pg_class WHERE relkind IN ('r','p'))/current_setting('max_connections')::int;

..probably with a fudge factor of +10 for any system process (and due to
integer truncation).

Someone might say that pg_upgrade or pg_dump could check for that specifically..

Justin


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Re: shared memory size during upgrade pgsql with partitions (max_locks_per_transaction)

Piotr Włodarczyk
>> On Tue, Dec 17, 2019 at 08:03:41PM +0000, Piotr Włodarczyk wrote:
>> Currently we're working on PSQL 11.5 and we're trying upgrade to 12.1.
>>
>> During that we have a problem:
>>
>> command: "/usr/pgsql-12/bin/pg_dump" --host /cluster/postgresql --port
50432
>> --username postgres --schema-only --quote-all-identifiers
--binary-upgrade
>> --format=custom  --file="pg_upgrade_dump_281535902.custom"
'dbname=sprint'
>> >> "pg_upgrade_dump_281535902.log" 2> &1
>> pg_dump: error: query failed: ERROR:  out of shared memory
>> HINT:  You might need to increase max_locks_per_transaction.
>> pg_dump: error: query was: LOCK TABLE
>> "some_schemaa"."table_part_80000000_2018q3" IN ACCESS SHARE MODE
>>
>> On current instance we have about one thousand of partitions, partitioned
in
>> two levels: first by id_product, and second level by quarter of the year,
as
>> you can see on above log.
>>
>> How have we to calculate shared memory, and (eventually
>> max_locks_per_transaction) to be fit to the limits during upgrade?
>
>
>
> Great question.  Clearly, if you can run that (or similar) pg_dump
command,
> then you can pg_upgrade.  I think you could also do pg_upgrade --check,

pg_upgrade --check doesn't prompt any error or warning

>
>
>
> The query looks like
> FROM pg_class c...
> WHERE c.relkind in ('%c', '%c', '%c', '%c', '%c', '%c',
'%c') "

>
>
>
> ..and then does:
>
>
>
>                if (tblinfo[i].dobj.dump &&
>                        (tblinfo[i].relkind == RELKIND_RELATION ||
>                         tblinfo-> relkind == RELKIND_PARTITIONED_TABLE) &&
>                        (tblinfo[i].dobj.dump &
DUMP_COMPONENTS_REQUIRING_LOCK))
>                {
>                        resetPQExpBuffer(query);
>                        appendPQExpBuffer(query,
>                                                          "LOCK TABLE %s IN
ACCESS SHARE MODE",
>
fmtQualifiedDumpable(&tblinfo[i]));

>                        ExecuteSqlStatement(fout, query-> data);
>                }
>
>
>
> ..then filters by -N/-n/-t/-T (which doesn't apply to pg_upgrade):
>                        selectDumpableTable(&tblinfo[i], fout);
>
>
>
> So it looks like COUNT(1) FROM pg_class WHERE relkind IN ('r','p') should
do it.
>
>
>
> But actually, during pg_upgrade, since nothing else is running, you
actually
> have max_connections*max_locks_per_transaction total locks.
>
>
>
> Said differently, I think you could set max_locks_per_transaction to:
> SELECT (SELECT COUNT(1) FROM pg_class WHERE relkind IN
('r','p'))/current_setting('max_connections')::int;
>
>
>
> ..probably with a fudge factor of +10 for any system process (and due to
> integer truncation).
>
>
>
> Someone might say that pg_upgrade or pg_dump could check for that
specifically..

Yes, and temporarily increase, or HINT how to calculate proper value.

>
>
>
> Justin
>
>

We realized that the problem is with pg_dump doing during pg_upgreade.

Now we're after upgrade and we can't check Yours calculation. We simply
increased max_connections until migration passed :)

I'll try to check it on empty, fake database.

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