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Stop demanding that top xact must be seen before subxact in decoding.

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Manifested as

ERROR:  subtransaction logged without previous top-level txn record

this check forbids legit behaviours like
 - First xl_xact_assignment record is beyond reading, i.e. earlier
   restart_lsn.
 - After restart_lsn there is some change of a subxact.
 - After that, there is second xl_xact_assignment (for another subxact)
   revealing the relationship between top and first subxact.

Such a transaction won't be streamed anyway because we hadn't seen it in
full.  Saying for sure whether xact of some record encountered after
the snapshot was deserialized can be streamed or not requires to know
whether it wrote something before deserialization point --if yes, it
hasn't been seen in full and can't be decoded. Snapshot doesn't have such
info, so there is no easy way to relax the check.

Reported-by: Hsu, John
Diagnosed-by: Arseny Sher
Author: Arseny Sher, Amit Kapila
Reviewed-by: Amit Kapila, Dilip Kumar
Backpatch-through: 9.5
Discussion: https://postgr.es/m/AB5978B2-1772-4FEE-A245-74C91704ECB0@amazon.com
This commit is contained in:
Amit Kapila
2020-02-19 08:27:15 +05:30
parent 6da7d36305
commit 59112f2355
4 changed files with 103 additions and 4 deletions
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2
contrib/test_decoding/Makefile
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@ -7,7 +7,7 @@ REGRESS = ddl xact rewrite toast permissions decoding_in_xact \
decoding_into_rel binary prepared replorigin time messages \
spill slot truncate
ISOLATION = mxact delayed_startup ondisk_startup concurrent_ddl_dml \
oldest_xmin snapshot_transfer
oldest_xmin snapshot_transfer subxact_without_top
REGRESS_OPTS = --temp-config $(top_srcdir)/contrib/test_decoding/logical.conf
ISOLATION_OPTS = --temp-config $(top_srcdir)/contrib/test_decoding/logical.conf