Fix leaking of small spilled subtransactions during logical decoding.

anarazel · anarazel · commit a27c566c77f8 · 2017-06-18T19:14:09.000-07:00
When, during logical decoding, a transaction gets too big, it's contents get spilled to disk. Not just the top-transaction gets spilled, but *also* all of its subtransactions, even if they're not that large themselves. Unfortunately we didn't clean up such small spilled subtransactions from disk. Fix that, by keeping better track of whether a transaction has been spilled to disk. Author: Andres Freund Reported-By: Dmitriy Sarafannikov, Fabrízio de Royes Mello Discussion: https://postgr.es/m/1457621358.355011041@f382.i.mail.ru https://postgr.es/m/CAFcNs+qNMhNYii4nxpO6gqsndiyxNDYV0S=JNq0v_sEE+9PHXg@mail.gmail.com Backpatch: 9.4-, where logical decoding was introduced
diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
@@ -871,7 +871,7 @@ ReorderBufferIterTXNInit(ReorderBuffer *rb, ReorderBufferTXN *txn)
 	{
 		ReorderBufferChange *cur_change;
 
-		if (txn->nentries != txn->nentries_mem)
+		if (txn->serialized)
 		{
 			/* serialize remaining changes */
 			ReorderBufferSerializeTXN(rb, txn);
@@ -900,7 +900,7 @@ ReorderBufferIterTXNInit(ReorderBuffer *rb, ReorderBufferTXN *txn)
 		{
 			ReorderBufferChange *cur_change;
 
-			if (cur_txn->nentries != cur_txn->nentries_mem)
+			if (cur_txn->serialized)
 			{
 				/* serialize remaining changes */
 				ReorderBufferSerializeTXN(rb, cur_txn);
@@ -1122,7 +1122,7 @@ ReorderBufferCleanupTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
 	Assert(found);
 
 	/* remove entries spilled to disk */
-	if (txn->nentries != txn->nentries_mem)
+	if (txn->serialized)
 		ReorderBufferRestoreCleanup(rb, txn);
 
 	/* deallocate */
@@ -2014,6 +2014,7 @@ ReorderBufferSerializeTXN(ReorderBuffer *rb, ReorderBufferTXN *txn)
 	Assert(spilled == txn->nentries_mem);
 	Assert(dlist_is_empty(&txn->changes));
 	txn->nentries_mem = 0;
+	txn->serialized = true;
 
 	if (fd != -1)
 		CloseTransientFile(fd);
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
@@ -193,6 +193,15 @@ typedef struct ReorderBufferTXN
 	 */
 	uint64		nentries_mem;
 
+	/*
+	 * Has this transaction been spilled to disk?  It's not always possible to
+	 * deduce that fact by comparing nentries with nentries_mem, because
+	 * e.g. subtransactions of a large transaction might get serialized
+	 * together with the parent - if they're restored to memory they'd have
+	 * nentries_mem == nentries.
+	 */
+	bool		serialized;
+
 	/*
 	 * List of ReorderBufferChange structs, including new Snapshots and new
 	 * CommandIds
