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Re: Column Filtering in Logical Replication

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Rahila Syed <rahilasyed90@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Tomas Vondra <tomas.vondra@enterprisedb.com>, Peter Smith <smithpb2250@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2021-09-06T19:16:03Z
Lists: pgsql-hackers 
The code in get_rel_sync_entry() changes current memory context to
CacheMemoryContext, then does a bunch of memory-leaking things.  This is
not good, because that memory context has to be very carefully managed
to avoid permanent memory leaks.  I suppose you added that because you
need something -- probably entry->att_map -- to survive memory context
resets, but if so then you need to change to CacheMemoryContext only
when that memory is allocated, not other chunks of memory.  I suspect
you can fix this by moving the MemoryContextSwitchTo() to just before
calling get_table_columnset; then all the leaky thinkgs are done in
whatever the original memory context is, which is fine.

(However, you also need to make sure that ->att_map is carefully freed
at the right time.  It looks like this already happens in
rel_sync_cache_relation_cb, but is rel_sync_cache_publication_cb
correct?  And in get_rel_sync_entry() itself, what if the entry already
has att_map -- should it be freed prior to allocating another one?)

By the way, I notice that your patch doesn't add documentation changes,
which are of course necessary.



/me is left wondering about PGOutputData->publication_names memory
handling ...

-- 
Álvaro Herrera              Valdivia, Chile  —  https://www.EnterpriseDB.com/

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Doc: Explain about Column List feature.

  2. Doc: fix column list vs. replica identity rules.

  3. Prohibit combining publications with different column lists.

  4. Fix the check to limit sync workers.

  5. Wait for subscription to sync in t/031_column_list.sql

  6. Move prattrs to the pg_publication_rel section in docs

  7. Allow specifying column lists for logical replication

  8. Fix row filters with multiple publications

  9. Fix publish_as_relid with multiple publications

  10. Add some additional tests for row filters in logical replication.

  11. Add index on pg_publication_rel.prpubid

  12. Avoid using DefElemAction in AlterPublicationStmt

  13. Small cleanups related to PUBLICATION framework code

  14. Add PublicationTable and PublicationRelInfo structs

  15. Fix various concurrency issues in logical replication worker launching