doc: clarify when row-level locks are released

They are released just like table-level locks.  Also clean up wording.
(Uses wording "rolled back to".)

Reported-by: [email protected]
Discussion: https://postgr.es/m/158074944048.1095.4309647363871637715@wrigleys.postgresql.org

Backpatch-through: 9.5

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
index f8c9655111978760da1a790fd41f684014b37bb4..ecff9474c8edd8313dc0f779061989bdf2a92145 100644 (file)
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -1039,7 +1039,7 @@ ERROR:  could not serialize access due to read/write dependencies among transact
      
 
    
-    Once acquired, a lock is normally held till end of transaction.  But if a
+    Once acquired, a lock is normally held until the end of the transaction.  But if a
     lock is acquired after establishing a savepoint, the lock is released
     immediately if the savepoint is rolled back to.  This is consistent with
     the principle that ROLLBACK cancels all effects of the
@@ -1178,7 +1178,10 @@ ERROR:  could not serialize access due to read/write dependencies among transact
      conflicting locks on the same row, even in different subtransactions;
      but other than that, two transactions can never hold conflicting locks
      on the same row.  Row-level locks do not affect data querying; they
-     block only writers and lockers to the same row.
+     block only writers and lockers to the same
+     row.  Row-level locks are released at transaction end or during
+     savepoint rollback, just like table-level locks.
+