Update transaction README for persistent multixacts

Multixacts are now maintained during recovery, but the README didn't get
the memo.  Backpatch to 9.3, where the divergence was introduced.

diff --git a/src/backend/access/transam/README b/src/backend/access/transam/README
index f83526ccc36d7d09bff6e0fbdeef0138653cb3af..d86a911afe000edae07560a74ca65ff0fb08bfb9 100644 (file)
--- a/src/backend/access/transam/README
+++ b/src/backend/access/transam/README
@@ -817,10 +817,7 @@ parent transaction to complete.
 
 Not all transactional behaviour is emulated, for example we do not insert
 a transaction entry into the lock table, nor do we maintain the transaction
-stack in memory. Clog entries are made normally. Multixact is not maintained
-because its purpose is to record tuple level locks that an application has
-requested to prevent other tuple locks. Since tuple locks cannot be obtained at
-all, there is never any conflict and so there is no reason to update multixact.
+stack in memory. Clog and multixact entries are made normally.
 Subtrans is maintained during recovery but the details of the transaction
 tree are ignored and all subtransactions reference the top-level TransactionId
 directly. Since commit is atomic this provides correct lock wait behaviour