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Update the docs and comments for decoding of prepared xacts.

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Commit a271a1b50e introduced decoding at prepare time in ReorderBuffer.
This can lead to deadlock for out-of-core logical replication solutions
that uses this feature to build distributed 2PC in case such transactions
lock [user] catalog tables exclusively. They need to inform users to not
have locks on catalog tables (via explicit LOCK command) in such
transactions.

Reported-by: Andres Freund
Discussion: https://postgr.es/m/20210222222847.tpnb6eg3yiykzpky@alap3.anarazel.de
This commit is contained in:
Amit Kapila
2021-03-01 08:14:33 +05:30
parent 6148656a0b
commit b4e3dc7fd4
2 changed files with 38 additions and 0 deletions
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24
doc/src/sgml/logicaldecoding.sgml
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@ -1228,5 +1228,29 @@ stream_commit_cb(...); <-- commit of the streamed transaction
that name pattern will not be decoded as a two-phase commit transaction.
</para>
<para>
The users that want to decode prepared transactions need to be careful about
below mentioned points:
<itemizedlist>
<listitem>
<para>
If the prepared transaction has locked [user] catalog tables exclusively
then decoding prepare can block till the main transaction is committed.
</para>
</listitem>
<listitem>
<para>
The logical replication solution that builds distributed two phase commit
using this feature can deadlock if the prepared transaction has locked
[user] catalog tables exclusively. They need to inform users to not have
locks on catalog tables (via explicit <command>LOCK</command> command) in
such transactions.
</para>
</listitem>
</itemizedlist>
</para>
</sect1>
</chapter>