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Logical decoding of sequences

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This extends the logical decoding to also decode sequence increments.
We differentiate between sequences created in the current (in-progress)
transaction, and sequences created earlier. This mixed behavior is
necessary because while sequences are not transactional (increments are
not subject to ROLLBACK), relfilenode changes are. So we do this:

* Changes for sequences created in the same top-level transaction are
  treated as transactional, i.e. just like any other change from that
  transaction, and discarded in case of a rollback.

* Changes for sequences created earlier are applied immediately, as if
  performed outside any transaction. This applies also after ALTER
  SEQUENCE, which may create a new relfilenode.

Moreover, if we ever get support for DDL replication, the sequence
won't exist until the transaction gets applied.

Sequences created in the current transaction are tracked in a simple
hash table, identified by a relfilenode. That means a sequence may
already exist, but if a transaction does ALTER SEQUENCE then the
increments for the new relfilenode will be treated as transactional.

For each relfilenode we track the XID of (sub)transaction that created
it, which is needed for cleanup at transaction end. We don't need to
check the XID to decide if an increment is transactional - if we find a
match in the hash table, it has to be the same transaction.

This requires two minor changes to WAL-logging. Firstly, we need to
ensure the sequence record has a valid XID - until now the the increment
might have XID 0 if it was the first change in a subxact. But the
sequence might have been created in the same top-level transaction. So
we ensure the XID is assigned when WAL-logging increments.

The other change is addition of "created" flag, marking increments for
newly created relfilenodes. This makes it easier to maintain the hash
table of sequences that need transactional handling.
Note: This is needed because of subxacts. A XID 0 might still have the
sequence created in a different subxact of the same top-level xact.

This does not include any changes to test_decoding and/or the built-in
replication - those will be committed in separate patches.

A patch adding decoding of sequences was originally submitted by Cary
Huang. This commit reworks various important aspects (e.g. the WAL
logging and transactional/non-transactional handling). However, the
original patch and reviews were very useful.

Author: Tomas Vondra, Cary Huang
Reviewed-by: Peter Eisentraut, Hannu Krosing, Andres Freund
Discussion: https://postgr.es/m/d045f3c2-6cfb-06d3-5540-e63c320df8bc@enterprisedb.com
Discussion: https://postgr.es/m/1710ed7e13b.cd7177461430746.3372264562543607781@highgo.ca
This commit is contained in:
Tomas Vondra
2022-02-10 18:43:28 +01:00
parent 0d4513b613
commit 0da92dc530
10 changed files with 786 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

88
src/backend/replication/logical/logical.c
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@ -73,6 +73,10 @@ static void truncate_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
static void message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
XLogRecPtr message_lsn, bool transactional,
const char *prefix, Size message_size, const char *message);
static void sequence_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
XLogRecPtr sequence_lsn, Relation rel,
bool transactional,
int64 last_value, int64 log_cnt, bool is_called);
/* streaming callbacks */
static void stream_start_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
@ -90,6 +94,10 @@ static void stream_change_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn
static void stream_message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
XLogRecPtr message_lsn, bool transactional,
const char *prefix, Size message_size, const char *message);
static void stream_sequence_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
XLogRecPtr sequence_lsn, Relation rel,
bool transactional,
int64 last_value, int64 log_cnt, bool is_called);
static void stream_truncate_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
int nrelations, Relation relations[], ReorderBufferChange *change);
@ -218,6 +226,7 @@ StartupDecodingContext(List *output_plugin_options,
ctx->reorder->apply_truncate = truncate_cb_wrapper;
ctx->reorder->commit = commit_cb_wrapper;
ctx->reorder->message = message_cb_wrapper;
ctx->reorder->sequence = sequence_cb_wrapper;
/*
* To support streaming, we require start/stop/abort/commit/change
@ -234,6 +243,7 @@ StartupDecodingContext(List *output_plugin_options,
(ctx->callbacks.stream_commit_cb != NULL) ||
(ctx->callbacks.stream_change_cb != NULL) ||
(ctx->callbacks.stream_message_cb != NULL) ||
(ctx->callbacks.stream_sequence_cb != NULL) ||
(ctx->callbacks.stream_truncate_cb != NULL);
/*
@ -251,6 +261,7 @@ StartupDecodingContext(List *output_plugin_options,
ctx->reorder->stream_commit = stream_commit_cb_wrapper;
ctx->reorder->stream_change = stream_change_cb_wrapper;
ctx->reorder->stream_message = stream_message_cb_wrapper;
ctx->reorder->stream_sequence = stream_sequence_cb_wrapper;
ctx->reorder->stream_truncate = stream_truncate_cb_wrapper;
@ -1203,6 +1214,42 @@ message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
error_context_stack = errcallback.previous;
}
static void
sequence_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
XLogRecPtr sequence_lsn, Relation rel, bool transactional,
int64 last_value, int64 log_cnt, bool is_called)
{
LogicalDecodingContext *ctx = cache->private_data;
LogicalErrorCallbackState state;
ErrorContextCallback errcallback;
Assert(!ctx->fast_forward);
if (ctx->callbacks.sequence_cb == NULL)
return;
/* Push callback + info on the error context stack */
state.ctx = ctx;
state.callback_name = "sequence";
state.report_location = sequence_lsn;
errcallback.callback = output_plugin_error_callback;
errcallback.arg = (void *) &state;
errcallback.previous = error_context_stack;
error_context_stack = &errcallback;
/* set output state */
ctx->accept_writes = true;
ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId;
ctx->write_location = sequence_lsn;
/* do the actual work: call callback */
ctx->callbacks.sequence_cb(ctx, txn, sequence_lsn, rel, transactional,
last_value, log_cnt, is_called);
/* Pop the error context stack */
error_context_stack = errcallback.previous;
}
static void
stream_start_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
XLogRecPtr first_lsn)
@ -1508,6 +1555,47 @@ stream_message_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
error_context_stack = errcallback.previous;
}
static void
stream_sequence_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
XLogRecPtr sequence_lsn, Relation rel,
bool transactional,
int64 last_value, int64 log_cnt, bool is_called)
{
LogicalDecodingContext *ctx = cache->private_data;
LogicalErrorCallbackState state;
ErrorContextCallback errcallback;
Assert(!ctx->fast_forward);
/* We're only supposed to call this when streaming is supported. */
Assert(ctx->streaming);
/* this callback is optional */
if (ctx->callbacks.stream_sequence_cb == NULL)
return;
/* Push callback + info on the error context stack */
state.ctx = ctx;
state.callback_name = "stream_sequence";
state.report_location = sequence_lsn;
errcallback.callback = output_plugin_error_callback;
errcallback.arg = (void *) &state;
errcallback.previous = error_context_stack;
error_context_stack = &errcallback;
/* set output state */
ctx->accept_writes = true;
ctx->write_xid = txn != NULL ? txn->xid : InvalidTransactionId;
ctx->write_location = sequence_lsn;
/* do the actual work: call callback */
ctx->callbacks.sequence_cb(ctx, txn, sequence_lsn, rel, transactional,
last_value, log_cnt, is_called);
/* Pop the error context stack */
error_context_stack = errcallback.previous;
}
static void
stream_truncate_cb_wrapper(ReorderBuffer *cache, ReorderBufferTXN *txn,
int nrelations, Relation relations[],