Re: [HACKERS] Help required to debug pg_repack breaking logical replication
On Sat, Oct 7, 2017 at 2:37 PM, Daniele Varrazzo wrote: > (with a > custom addition to update the relfrozenxid which seems backwards to me > as it sets the older frozen xid on the new table [3]). > > [3] https://github.com/reorg/pg_repack/issues/152 Wow. That's really bad. It will corrupt your database. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Help required to debug pg_repack breaking logical replication
On 08/10/17 15:21, Craig Ringer wrote: > On 8 October 2017 at 02:37, Daniele Varrazzo > wrote: >> Hello, >> >> we have been reported, and I have experienced a couple of times, >> pg_repack breaking logical replication. >> >> - https://github.com/reorg/pg_repack/issues/135 >> - https://github.com/2ndQuadrant/pglogical/issues/113 > > Yeah, I was going to say I've seen reports of this with pglogical, but > I see you've linked to them. > > I haven't had a chance to look into it though, and haven't had a > suitable reproducible test case. > >> In the above issue #113, Petr Jelinek commented: >> >>> From quick look at pg_repack, the way it does table rewrite is almost >>> guaranteed >>> to break logical decoding unless there is zero unconsumed changes for a >>> given table >>> as it does not build the necessary mappings info for logical decoding that >>> standard >>> heap rewrite in postgres does. >> >> unfortunately he didn't follow up to further details requests. > > At a guess he's referring to src/backend/access/heap/rewriteheap.c . > > I'd explain better if I understood what was going on myself, but I > haven't really understood the logical decoding parts of that code. > >> - Is Petr diagnosis right and freezing of logical replication is to be >> blamed to missing mapping? >> - Can you suggest a test to reproduce the issue reliably? >> - What are mapped relations anyway? > > I can't immediately give you the answers you seek, but start by > studying src/backend/access/heap/rewriteheap.c . Notably > logical_end_heap_rewrite, logical_rewrite_heap_tuple, > logical_begin_heap_rewrite. > Yes that's exactly it. When table is rewritten we need to create mapping for every tuple that was created or removed (ie, insert, update or delete operation happened on it) since the oldest replication slot xmin for logical decoding to continue to work on that table after the rewrite. And pg_repack doesn't create that mapping. -- Petr Jelinek http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Help required to debug pg_repack breaking logical replication
On 8 October 2017 at 02:37, Daniele Varrazzo wrote: > Hello, > > we have been reported, and I have experienced a couple of times, > pg_repack breaking logical replication. > > - https://github.com/reorg/pg_repack/issues/135 > - https://github.com/2ndQuadrant/pglogical/issues/113 Yeah, I was going to say I've seen reports of this with pglogical, but I see you've linked to them. I haven't had a chance to look into it though, and haven't had a suitable reproducible test case. > In the above issue #113, Petr Jelinek commented: > >> From quick look at pg_repack, the way it does table rewrite is almost >> guaranteed >> to break logical decoding unless there is zero unconsumed changes for a >> given table >> as it does not build the necessary mappings info for logical decoding that >> standard >> heap rewrite in postgres does. > > unfortunately he didn't follow up to further details requests. At a guess he's referring to src/backend/access/heap/rewriteheap.c . I'd explain better if I understood what was going on myself, but I haven't really understood the logical decoding parts of that code. > - Is Petr diagnosis right and freezing of logical replication is to be > blamed to missing mapping? > - Can you suggest a test to reproduce the issue reliably? > - What are mapped relations anyway? I can't immediately give you the answers you seek, but start by studying src/backend/access/heap/rewriteheap.c . Notably logical_end_heap_rewrite, logical_rewrite_heap_tuple, logical_begin_heap_rewrite. At a wild "I haven't read any of the relevant code in detail yet" stab in the dark, pg_repack is failing to do the bookkeeping required by logical decoding around relfilenode changes, cmin/cmax, etc. -- Craig Ringer http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
