Use psqlscan only when query string is large.

This is a follow-up commit to 48da8715bf403965507eef0321c0ab10054ac71c.
Discussion: https://www.pgpool.net/pipermail/pgpool-hackers/2023-April/004320.html

diff --git a/src/protocol/pool_proto_modules.c b/src/protocol/pool_proto_modules.c
index 34edd509665e03d7a70af54275e0e41e8e38f8ba..c1237e043731924136370fd7e92acb2090d1f72d 100644 (file)
--- a/src/protocol/pool_proto_modules.c
+++ b/src/protocol/pool_proto_modules.c
@@ -201,6 +201,12 @@ SimpleQuery(POOL_CONNECTION * frontend,
        bool            error;
        bool            use_minimal;
 
+/*
+ * If query string is shorter than this, we do not run
+ * multi_statement_query() to avoid its overhead.
+ */
+#define        LENGTHY_QUERY_STRING    1024*10
+
        /* Get session context */
        session_context = pool_get_session_context(false);
 
@@ -260,31 +266,48 @@ SimpleQuery(POOL_CONNECTION * frontend,
        query_context = pool_init_query_context();
        MemoryContext old_context = MemoryContextSwitchTo(query_context->memory_context);
 
-       /*
-        * Check whether the query is multi statement or not.
-        */
-       if (multi_statement_query(contents))
-       {
-               elog(DEBUG5, "multi statement query found");
-               query_context->is_multi_statement = true;
-               use_minimal = false;    /* never use minimal parser */
-       }
-       else
+       /* Is query string long? */
+       if (len > LENGTHY_QUERY_STRING)
        {
-               query_context->is_multi_statement = false;
                /*
-                * Do not use minimal parser if we are in native replication or
-                * snapshot isolation mode.
+                * Check whether the query is multi statement or not.
                 */
-               if (REPLICATION)
-                       use_minimal = false;
+               if (multi_statement_query(contents))
+               {
+                       elog(DEBUG5, "multi statement query found");
+                       query_context->is_multi_statement = true;
+                       use_minimal = false;    /* never use minimal parser */
+               }
                else
-                       use_minimal = true;
+               {
+                       query_context->is_multi_statement = false;
+                       /*
+                        * Do not use minimal parser if we are in native replication or
+                        * snapshot isolation mode.
+                        */
+                       if (REPLICATION)
+                               use_minimal = false;
+                       else
+                               use_minimal = true;
+               }
+       }
+       else
+       {
+               use_minimal = false;
        }
 
-       /* parse SQL string */
+       /* Parse SQL string */
        parse_tree_list = raw_parser(contents, RAW_PARSE_DEFAULT, len, &error, use_minimal);
 
+       if (len <= LENGTHY_QUERY_STRING)
+       {
+               /* we have not checked whether multi-statement query or not */
+               if (list_length(parse_tree_list) > 1)
+                       query_context->is_multi_statement = true;
+               else
+                       query_context->is_multi_statement = false;
+       }
+
        if (parse_tree_list == NIL)
        {
                /* is the query empty? */