Issue #27: Add tests and comment.

Author: Maxim Orlov

expected/pg_variables_trans.out

@@ -3510,3 +3510,49 @@ SELECT pgv_free();
 
 (1 row)
 
+-- take #4
+SELECT pgv_insert('test', 'x', ROW (1::int, 2::int), TRUE);
+ pgv_insert 
+------------
+ 
+(1 row)
+
+SELECT pgv_insert('test', 'x', ROW (2::int, 3::int), TRUE);
+ pgv_insert 
+------------
+ 
+(1 row)
+
+BEGIN;
+DECLARE r1_cur CURSOR FOR SELECT pgv_select('test', 'x');
+SAVEPOINT sp1;
+FETCH 1 in r1_cur;
+ pgv_select 
+------------
+ (1,2)
+(1 row)
+
+ROLLBACK TO SAVEPOINT sp1;
+COMMIT;
+BEGIN;
+DECLARE r1_cur CURSOR FOR SELECT pgv_select('test', 'x');
+SAVEPOINT sp1;
+FETCH 2 in r1_cur;
+ pgv_select 
+------------
+ (1,2)
+ (2,3)
+(2 rows)
+
+ROLLBACK TO SAVEPOINT sp1;
+COMMIT;
+BEGIN;
+SAVEPOINT sp1;
+SELECT pgv_select('test', 'x') LIMIT 1;
+ pgv_select 
+------------
+ (1,2)
+(1 row)
+
+ROLLBACK TO SAVEPOINT sp1;
+COMMIT;

pg_variables.c

@@ -129,7 +129,20 @@ static ExecutorEnd_hook_type prev_ExecutorEnd = NULL;
 static dlist_head *changesStack = NULL;
 static MemoryContext changesStackContext = NULL;
 
-/* List to store all the running hash_seq_search scan for hash table */
+/*
+ * List to store all the running hash_seq_search scan for hash table.
+ *
+ * NOTE: In function variable_select we use hash_seq_search to find next tuple.
+ * So, in case user do not get all the data from set at once (use cursors or
+ * LIMIT) we have to call hash_seq_term to not to leak hash_seq_search scans.
+ *
+ * For doing this, we alloc all of the rstats in the TopTransactionContext and
+ * save pointers to the rstats into list. Once transaction ended (commited or
+ * aborted) we clear all the "active" hash_seq_search by calling hash_seq_term.
+ *
+ * TopTransactionContext is handy here, becouse it wount be reset by the time
+ * pgvTransCallback is called.
+ */
 static List *rstats = NIL; 
 
 /* Returns a lists of packages and variables changed at current subxact level */

sql/pg_variables_trans.sql

@@ -1007,3 +1007,26 @@ COMMIT;
 SELECT pgv_select('test', 'z3');
 
 SELECT pgv_free();
+-- take #4
+SELECT pgv_insert('test', 'x', ROW (1::int, 2::int), TRUE);
+SELECT pgv_insert('test', 'x', ROW (2::int, 3::int), TRUE);
+
+BEGIN;
+DECLARE r1_cur CURSOR FOR SELECT pgv_select('test', 'x');
+SAVEPOINT sp1;
+FETCH 1 in r1_cur;
+ROLLBACK TO SAVEPOINT sp1;
+COMMIT;
+
+BEGIN;
+DECLARE r1_cur CURSOR FOR SELECT pgv_select('test', 'x');
+SAVEPOINT sp1;
+FETCH 2 in r1_cur;
+ROLLBACK TO SAVEPOINT sp1;
+COMMIT;
+
+BEGIN;
+SAVEPOINT sp1;
+SELECT pgv_select('test', 'x') LIMIT 1;
+ROLLBACK TO SAVEPOINT sp1;
+COMMIT;