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| author | Amit Kapila <akapila@postgresql.org> | 2021-03-01 08:14:33 +0530 |
|---|---|---|
| committer | Amit Kapila <akapila@postgresql.org> | 2021-03-01 08:14:33 +0530 |
| commit | b4e3dc7fd420cdc2287f30a638c4affd071f01b2 (patch) | |
| tree | 9b16c0843a81482506e2e4ce4afca9d06ce610d9 | |
| parent | 6148656a0be1c6245fbcfcbbeb87541f1b173162 (diff) | |
| download | postgresql-b4e3dc7fd420cdc2287f30a638c4affd071f01b2.tar.gz postgresql-b4e3dc7fd420cdc2287f30a638c4affd071f01b2.zip | |
Update the docs and comments for decoding of prepared xacts.
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
| -rw-r--r-- | doc/src/sgml/logicaldecoding.sgml | 24 | ||||
| -rw-r--r-- | src/backend/replication/logical/decode.c | 14 |
2 files changed, 38 insertions, 0 deletions
diff --git a/doc/src/sgml/logicaldecoding.sgml b/doc/src/sgml/logicaldecoding.sgml index 6455664cb4f..85c55d64125 100644 --- a/doc/src/sgml/logicaldecoding.sgml +++ b/doc/src/sgml/logicaldecoding.sgml @@ -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> diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c index afa1df00d0e..657cb4af1e3 100644 --- a/src/backend/replication/logical/decode.c +++ b/src/backend/replication/logical/decode.c @@ -362,6 +362,20 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf) break; } + /* + * Note that if the prepared transaction has locked [user] + * catalog tables exclusively then decoding prepare can block + * till the main transaction is committed because it needs to + * lock the catalog tables. + * + * XXX Now, this can even lead to a deadlock if the prepare + * transaction is waiting to get it logically replicated for + * distributed 2PC. Currently, we don't have an in-core + * implementation of prepares for distributed 2PC but some + * out-of-core logical replication solution can have such an + * implementation. They need to inform users to not have locks + * on catalog tables in such transactions. + */ DecodePrepare(ctx, buf, &parsed); break; } |