From: | Kuntal Ghosh <kuntalghosh(dot)2007(at)gmail(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com>, Alvaro Herrera from 2ndQuadrant <alvherre(at)alvh(dot)no-ip(dot)org>, Andres Freund <andres(at)anarazel(dot)de>, Juan José Santamaría Flecha <juanjo(dot)santamaria(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
Subject: | Re: logical decoding : exceeded maxAllocatedDescs for .spill files |
Date: | 2020-02-04 04:45:01 |
Message-ID: | CAGz5QCJZpiEiPx7z1tS4BhLbS8j9zJB+0g8Knj+1mn_7en6k8Q@mail.gmail.com |
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Lists: | pgsql-hackers |
On Sun, Jan 12, 2020 at 9:51 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)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;
>
I performed the same test in pg11 and reproduced the issue on the
commit prior to a4ccc1cef5a04 (Generational memory allocator).
ulimit -s 1024
ulimit -v 300000
wal_level = logical
max_replication_slots = 4
And executed the following code snippet (shared by Amit Khandekar
earlier in the thread).
SELECT pg_create_logical_replication_slot('test_slot',
'test_decoding');
CREATE TABLE decoding_test(x integer, y text);
do $$
BEGIN
FOR i IN 1..10 LOOP
BEGIN
INSERT INTO decoding_test(x) SELECT
generate_series(1,3000);
EXCEPTION
when division_by_zero then perform 'dummy';
END;
END LOOP;
END $$;
SELECT data from pg_logical_slot_get_changes('test_slot', NULL, NULL) LIMIT 10;
I got the following error:
ERROR: out of memory
DETAIL: Failed on request of size 8208.
After that, I applied the "Generational memory allocator" patch and
that solved the issue. From the error message, it is evident that the
underlying code is trying to allocate a MaxTupleSize memory for each
tuple. So, I re-introduced the following lines (which are removed by
a4ccc1cef5a04) on top of the patch:
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -417,6 +417,9 @@ ReorderBufferGetTupleBuf(ReorderBuffer *rb, Size tuple_len)
alloc_len = tuple_len + SizeofHeapTupleHeader;
+ if (alloc_len < MaxHeapTupleSize)
+ alloc_len = MaxHeapTupleSize;
And, the issue got reproduced with the same error:
WARNING: problem in Generation Tuples: number of free chunks 0 in
block 0x7fe9e9e74010 exceeds 1018 allocated
.....
ERROR: out of memory
DETAIL: Failed on request of size 8208.
I don't understand the code well enough to comment whether we can
back-patch only this part of the code. But, this seems to allocate a
huge amount of memory per chunk although the tuple is small.
Thoughts?
--
Thanks & Regards,
Kuntal Ghosh
EnterpriseDB: http://www.enterprisedb.com
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