Fix leaking of small spilled subtransactions during logical decoding.

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

1 files changed, 9 insertions, 0 deletions

diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index 9e209aef4fb..a7ebf293822 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -213,6 +213,15 @@ 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
 	 */