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Extend the output plugin API to allow decoding of prepared xacts.

Browse Source 
This adds six methods to the output plugin API, adding support for
streaming changes of two-phase transactions at prepare time.

* begin_prepare
* filter_prepare
* prepare
* commit_prepared
* rollback_prepared
* stream_prepare

Most of this is a simple extension of the existing methods, with the
semantic difference that the transaction is not yet committed and maybe
aborted later.

Until now two-phase transactions were translated into regular transactions
on the subscriber, and the GID was not forwarded to it. None of the
two-phase commands were communicated to the subscriber.

This patch provides the infrastructure for logical decoding plugins to be
informed of two-phase commands Like PREPARE TRANSACTION, COMMIT PREPARED
and ROLLBACK PREPARED commands with the corresponding GID.

This also extends the 'test_decoding' plugin, implementing these new
methods.

This commit simply adds these new APIs and the upcoming patch to "allow
the decoding at prepare time in ReorderBuffer" will use these APIs.

Author: Ajin Cherian and Amit Kapila based on previous work by Nikhil Sontakke and Stas Kelvich
Reviewed-by: Amit Kapila, Peter Smith, Sawada Masahiko, and Dilip Kumar
Discussion:
https://postgr.es/m/02DA5F5E-CECE-4D9C-8B4B-418077E2C010@postgrespro.ru
https://postgr.es/m/CAMGcDxeqEpWj3fTXwqhSwBdXd2RS9jzwWscO-XbeCfso6ts3+Q@mail.gmail.com
This commit is contained in:
Amit Kapila
2020-12-30 16:17:26 +05:30
parent fa744697c7
commit 0aa8a01d04
7 changed files with 744 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

167
contrib/test_decoding/test_decoding.c
View File

@ -76,6 +76,20 @@ static void pg_decode_message(LogicalDecodingContext *ctx,
ReorderBufferTXN *txn, XLogRecPtr message_lsn,
bool transactional, const char *prefix,
Size sz, const char *message);
static bool pg_decode_filter_prepare(LogicalDecodingContext *ctx,
const char *gid);
static void pg_decode_begin_prepare_txn(LogicalDecodingContext *ctx,
ReorderBufferTXN *txn);
static void pg_decode_prepare_txn(LogicalDecodingContext *ctx,
ReorderBufferTXN *txn,
XLogRecPtr prepare_lsn);
static void pg_decode_commit_prepared_txn(LogicalDecodingContext *ctx,
ReorderBufferTXN *txn,
XLogRecPtr commit_lsn);
static void pg_decode_rollback_prepared_txn(LogicalDecodingContext *ctx,
ReorderBufferTXN *txn,
XLogRecPtr prepare_end_lsn,
TimestampTz prepare_time);
static void pg_decode_stream_start(LogicalDecodingContext *ctx,
ReorderBufferTXN *txn);
static void pg_output_stream_start(LogicalDecodingContext *ctx,
@ -87,6 +101,9 @@ static void pg_decode_stream_stop(LogicalDecodingContext *ctx,
static void pg_decode_stream_abort(LogicalDecodingContext *ctx,
ReorderBufferTXN *txn,
XLogRecPtr abort_lsn);
static void pg_decode_stream_prepare(LogicalDecodingContext *ctx,
ReorderBufferTXN *txn,
XLogRecPtr prepare_lsn);
static void pg_decode_stream_commit(LogicalDecodingContext *ctx,
ReorderBufferTXN *txn,
XLogRecPtr commit_lsn);
@ -123,9 +140,15 @@ _PG_output_plugin_init(OutputPluginCallbacks *cb)
cb->filter_by_origin_cb = pg_decode_filter;
cb->shutdown_cb = pg_decode_shutdown;
cb->message_cb = pg_decode_message;
cb->filter_prepare_cb = pg_decode_filter_prepare;
cb->begin_prepare_cb = pg_decode_begin_prepare_txn;
cb->prepare_cb = pg_decode_prepare_txn;
cb->commit_prepared_cb = pg_decode_commit_prepared_txn;
cb->rollback_prepared_cb = pg_decode_rollback_prepared_txn;
cb->stream_start_cb = pg_decode_stream_start;
cb->stream_stop_cb = pg_decode_stream_stop;
cb->stream_abort_cb = pg_decode_stream_abort;
cb->stream_prepare_cb = pg_decode_stream_prepare;
cb->stream_commit_cb = pg_decode_stream_commit;
cb->stream_change_cb = pg_decode_stream_change;
cb->stream_message_cb = pg_decode_stream_message;
@ -141,6 +164,7 @@ pg_decode_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
ListCell *option;
TestDecodingData *data;
bool enable_streaming = false;
bool enable_twophase = false;
data = palloc0(sizeof(TestDecodingData));
data->context = AllocSetContextCreate(ctx->context,
@ -241,6 +265,16 @@ pg_decode_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
errmsg("could not parse value \"%s\" for parameter \"%s\"",
strVal(elem->arg), elem->defname)));
}
else if (strcmp(elem->defname, "two-phase-commit") == 0)
{
if (elem->arg == NULL)
continue;
else if (!parse_bool(strVal(elem->arg), &enable_twophase))
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("could not parse value \"%s\" for parameter \"%s\"",
strVal(elem->arg), elem->defname)));
}
else
{
ereport(ERROR,
@ -252,6 +286,7 @@ pg_decode_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
}
ctx->streaming &= enable_streaming;
ctx->twophase &= enable_twophase;
}
/* cleanup this plugin's resources */
@ -320,6 +355,111 @@ pg_decode_commit_txn(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
OutputPluginWrite(ctx, true);
}
/* BEGIN PREPARE callback */
static void
pg_decode_begin_prepare_txn(LogicalDecodingContext *ctx, ReorderBufferTXN *txn)
{
TestDecodingData *data = ctx->output_plugin_private;
TestDecodingTxnData *txndata =
MemoryContextAllocZero(ctx->context, sizeof(TestDecodingTxnData));
txndata->xact_wrote_changes = false;
txn->output_plugin_private = txndata;
if (data->skip_empty_xacts)
return;
pg_output_begin(ctx, data, txn, true);
}
/* PREPARE callback */
static void
pg_decode_prepare_txn(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
XLogRecPtr prepare_lsn)
{
TestDecodingData *data = ctx->output_plugin_private;
TestDecodingTxnData *txndata = txn->output_plugin_private;
if (data->skip_empty_xacts && !txndata->xact_wrote_changes)
return;
OutputPluginPrepareWrite(ctx, true);
appendStringInfo(ctx->out, "PREPARE TRANSACTION %s",
quote_literal_cstr(txn->gid));
if (data->include_xids)
appendStringInfo(ctx->out, ", txid %u", txn->xid);
if (data->include_timestamp)
appendStringInfo(ctx->out, " (at %s)",
timestamptz_to_str(txn->commit_time));
OutputPluginWrite(ctx, true);
}
/* COMMIT PREPARED callback */
static void
pg_decode_commit_prepared_txn(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
XLogRecPtr commit_lsn)
{
TestDecodingData *data = ctx->output_plugin_private;
OutputPluginPrepareWrite(ctx, true);
appendStringInfo(ctx->out, "COMMIT PREPARED %s",
quote_literal_cstr(txn->gid));
if (data->include_xids)
appendStringInfo(ctx->out, ", txid %u", txn->xid);
if (data->include_timestamp)
appendStringInfo(ctx->out, " (at %s)",
timestamptz_to_str(txn->commit_time));
OutputPluginWrite(ctx, true);
}
/* ROLLBACK PREPARED callback */
static void
pg_decode_rollback_prepared_txn(LogicalDecodingContext *ctx,
ReorderBufferTXN *txn,
XLogRecPtr prepare_end_lsn,
TimestampTz prepare_time)
{
TestDecodingData *data = ctx->output_plugin_private;
OutputPluginPrepareWrite(ctx, true);
appendStringInfo(ctx->out, "ROLLBACK PREPARED %s",
quote_literal_cstr(txn->gid));
if (data->include_xids)
appendStringInfo(ctx->out, ", txid %u", txn->xid);
if (data->include_timestamp)
appendStringInfo(ctx->out, " (at %s)",
timestamptz_to_str(txn->commit_time));
OutputPluginWrite(ctx, true);
}
/*
* Filter out two-phase transactions.
*
* Each plugin can implement its own filtering logic. Here we demonstrate a
* simple logic by checking the GID. If the GID contains the "_nodecode"
* substring, then we filter it out.
*/
static bool
pg_decode_filter_prepare(LogicalDecodingContext *ctx, const char *gid)
{
if (strstr(gid, "_nodecode") != NULL)
return true;
return false;
}
static bool
pg_decode_filter(LogicalDecodingContext *ctx,
RepOriginId origin_id)
@ -701,6 +841,33 @@ pg_decode_stream_abort(LogicalDecodingContext *ctx,
OutputPluginWrite(ctx, true);
}
static void
pg_decode_stream_prepare(LogicalDecodingContext *ctx,
ReorderBufferTXN *txn,
XLogRecPtr prepare_lsn)
{
TestDecodingData *data = ctx->output_plugin_private;
TestDecodingTxnData *txndata = txn->output_plugin_private;
if (data->skip_empty_xacts && !txndata->xact_wrote_changes)
return;
OutputPluginPrepareWrite(ctx, true);
if (data->include_xids)
appendStringInfo(ctx->out, "preparing streamed transaction TXN %s, txid %u",
quote_literal_cstr(txn->gid), txn->xid);
else
appendStringInfo(ctx->out, "preparing streamed transaction %s",
quote_literal_cstr(txn->gid));
if (data->include_timestamp)
appendStringInfo(ctx->out, " (at %s)",
timestamptz_to_str(txn->commit_time));
OutputPluginWrite(ctx, true);
}
static void
pg_decode_stream_commit(LogicalDecodingContext *ctx,
ReorderBufferTXN *txn,