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Add support for prepared transactions to built-in logical replication.

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To add support for streaming transactions at prepare time into the
built-in logical replication, we need to do the following things:

* Modify the output plugin (pgoutput) to implement the new two-phase API
callbacks, by leveraging the extended replication protocol.

* Modify the replication apply worker, to properly handle two-phase
transactions by replaying them on prepare.

* Add a new SUBSCRIPTION option "two_phase" to allow users to enable
two-phase transactions. We enable the two_phase once the initial data sync
is over.

We however must explicitly disable replication of two-phase transactions
during replication slot creation, even if the plugin supports it. We
don't need to replicate the changes accumulated during this phase,
and moreover, we don't have a replication connection open so we don't know
where to send the data anyway.

The streaming option is not allowed with this new two_phase option. This
can be done as a separate patch.

We don't allow to toggle two_phase option of a subscription because it can
lead to an inconsistent replica. For the same reason, we don't allow to
refresh the publication once the two_phase is enabled for a subscription
unless copy_data option is false.

Author: Peter Smith, Ajin Cherian and Amit Kapila based on previous work by Nikhil Sontakke and Stas Kelvich
Reviewed-by: Amit Kapila, Sawada Masahiko, Vignesh C, Dilip Kumar, Takamichi Osumi, Greg Nancarrow
Tested-By: Haiying Tang
Discussion: https://postgr.es/m/02DA5F5E-CECE-4D9C-8B4B-418077E2C010@postgrespro.ru
Discussion: https://postgr.es/m/CAA4eK1+opiV4aFTmWWUF9h_32=HfPOW9vZASHarT0UA5oBrtGw@mail.gmail.com
This commit is contained in:
Amit Kapila
2021-07-14 07:33:50 +05:30
parent 6c9c283166
commit a8fd13cab0
43 changed files with 2382 additions and 191 deletions
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11
src/backend/replication/logical/decode.c
View File

@ -374,11 +374,10 @@ DecodeXactOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
*
* 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.
* distributed 2PC. This can be avoided by disallowing
* preparing transactions that have locked [user] catalog
* tables exclusively but as of now, we ask users not to do
* such an operation.
*/
DecodePrepare(ctx, buf, &parsed);
break;
@ -735,7 +734,7 @@ DecodeCommit(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
if (two_phase)
{
ReorderBufferFinishPrepared(ctx->reorder, xid, buf->origptr, buf->endptr,
SnapBuildInitialConsistentPoint(ctx->snapshot_builder),
SnapBuildGetTwoPhaseAt(ctx->snapshot_builder),
commit_time, origin_id, origin_lsn,
parsed->twophase_gid, true);
}