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Generic Messages for Logical Decoding

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API and mechanism to allow generic messages to be inserted into WAL that are
intended to be read by logical decoding plugins. This commit adds an optional
new callback to the logical decoding API.

Messages are either text or bytea. Messages can be transactional, or not, and
are identified by a prefix to allow multiple concurrent decoding plugins.

(Not to be confused with Generic WAL records, which are intended to allow crash
recovery of extensible objects.)

Author: Petr Jelinek and Andres Freund
Reviewers: Artur Zakirov, Tomas Vondra, Simon Riggs
Discussion: 5685F999.6010202@2ndquadrant.com
This commit is contained in:
Simon Riggs
2016-04-06 10:05:41 +01:00
parent 989be0810d
commit 3fe3511d05
27 changed files with 693 additions and 33 deletions
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121
src/backend/replication/logical/reorderbuffer.c
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@ -414,6 +414,14 @@ ReorderBufferReturnChange(ReorderBuffer *rb, ReorderBufferChange *change)
change->data.tp.oldtuple = NULL;
}
break;
case REORDER_BUFFER_CHANGE_MESSAGE:
if (change->data.msg.prefix != NULL)
pfree(change->data.msg.prefix);
change->data.msg.prefix = NULL;
if (change->data.msg.message != NULL)
pfree(change->data.msg.message);
change->data.msg.message = NULL;
break;
case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
if (change->data.snapshot)
{
@ -627,6 +635,61 @@ ReorderBufferQueueChange(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn,
ReorderBufferCheckSerializeTXN(rb, txn);
}
/*
* Queue message into a transaction so it can be processed upon commit.
*/
void
ReorderBufferQueueMessage(ReorderBuffer *rb, TransactionId xid,
Snapshot snapshot, XLogRecPtr lsn,
bool transactional, const char *prefix,
Size message_size, const char *message)
{
if (transactional)
{
MemoryContext oldcontext;
ReorderBufferChange *change;
Assert(xid != InvalidTransactionId);
oldcontext = MemoryContextSwitchTo(rb->context);
change = ReorderBufferGetChange(rb);
change->action = REORDER_BUFFER_CHANGE_MESSAGE;
change->data.msg.prefix = pstrdup(prefix);
change->data.msg.message_size = message_size;
change->data.msg.message = palloc(message_size);
memcpy(change->data.msg.message, message, message_size);
ReorderBufferQueueChange(rb, xid, lsn, change);
MemoryContextSwitchTo(oldcontext);
}
else
{
ReorderBufferTXN *txn = NULL;
volatile Snapshot snapshot_now = snapshot;
if (xid != InvalidTransactionId)
txn = ReorderBufferTXNByXid(rb, xid, true, NULL, lsn, true);
/* setup snapshot to allow catalog access */
SetupHistoricSnapshot(snapshot_now, NULL);
PG_TRY();
{
rb->message(rb, txn, lsn, false, prefix, message_size, message);
TeardownHistoricSnapshot(false);
}
PG_CATCH();
{
TeardownHistoricSnapshot(true);
PG_RE_THROW();
}
PG_END_TRY();
}
}
static void
AssertTXNLsnOrder(ReorderBuffer *rb)
{
@ -1493,6 +1556,13 @@ ReorderBufferCommit(ReorderBuffer *rb, TransactionId xid,
specinsert = change;
break;
case REORDER_BUFFER_CHANGE_MESSAGE:
rb->message(rb, txn, change->lsn, true,
change->data.msg.prefix,
change->data.msg.message_size,
change->data.msg.message);
break;
case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
/* get rid of the old */
TeardownHistoricSnapshot(false);
@ -2157,6 +2227,33 @@ ReorderBufferSerializeChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
memcpy(data, newtup->tuple.t_data, newlen);
data += newlen;
}
break;
}
case REORDER_BUFFER_CHANGE_MESSAGE:
{
char *data;
Size prefix_size = strlen(change->data.msg.prefix) + 1;
sz += prefix_size + change->data.msg.message_size +
sizeof(Size) + sizeof(Size);
ReorderBufferSerializeReserve(rb, sz);
data = ((char *) rb->outbuf) + sizeof(ReorderBufferDiskChange);
/* write the prefix including the size */
memcpy(data, &prefix_size, sizeof(Size));
data += sizeof(Size);
memcpy(data, change->data.msg.prefix,
prefix_size);
data += prefix_size;
/* write the message including the size */
memcpy(data, &change->data.msg.message_size, sizeof(Size));
data += sizeof(Size);
memcpy(data, change->data.msg.message,
change->data.msg.message_size);
data += change->data.msg.message_size;
break;
}
case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
@ -2415,6 +2512,30 @@ ReorderBufferRestoreChange(ReorderBuffer *rb, ReorderBufferTXN *txn,
}
break;
case REORDER_BUFFER_CHANGE_MESSAGE:
{
Size prefix_size;
/* read prefix */
memcpy(&prefix_size, data, sizeof(Size));
data += sizeof(Size);
change->data.msg.prefix = MemoryContextAlloc(rb->context,
prefix_size);
memcpy(change->data.msg.prefix, data, prefix_size);
Assert(change->data.msg.prefix[prefix_size-1] == '\0');
data += prefix_size;
/* read the messsage */
memcpy(&change->data.msg.message_size, data, sizeof(Size));
data += sizeof(Size);
change->data.msg.message = MemoryContextAlloc(rb->context,
change->data.msg.message_size);
memcpy(change->data.msg.message, data,
change->data.msg.message_size);
data += change->data.msg.message_size;
break;
}
case REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT:
{
Snapshot oldsnap;