branches/5.1: Identify SELECT statements by thd_sql_command() == SQLCOM_SELECT

instead of parsing the query string.  This fixes MySQL Bug #37885 without
us having to implement lexical analysis of SQL comments in yet another place.

thd_is_select(): A new predicate.

row_search_for_mysql(): Use thd_is_select().

Approved by Heikki.

handler/ha_innodb.cc

@@ -507,6 +507,18 @@ thd_has_edited_nontrans_tables(
 	return((ibool) thd_non_transactional_update((THD*) thd));
 }
 
+/**********************************************************************
+Returns true if the thread is executing a SELECT statement. */
+extern "C"
+ibool
+thd_is_select(
+/*==========*/
+				/* out: true if thd is executing SELECT */
+	const void*	thd)	/* in: thread handle (THD*) */
+{
+	return(thd_sql_command((const THD*) thd) == SQLCOM_SELECT);
+}
+
 /************************************************************************
 Obtain the InnoDB transaction of a MySQL thread. */
 inline

include/ha_prototypes.h

@@ -63,5 +63,14 @@ thd_has_edited_nontrans_tables(
 			been edited */
 	void*	thd);	/* in: thread handle (THD*) */
 
+/**********************************************************************
+Returns true if the thread is executing a SELECT statement. */
+
+ibool
+thd_is_select(
+/*==========*/
+				/* out: true if thd is executing SELECT */
+	const void*	thd);	/* in: thread handle (THD*) */
+
 #endif
 #endif

row/row0sel.c

@@ -32,6 +32,7 @@ Created 12/19/1997 Heikki Tuuri
 #include "row0mysql.h"
 #include "read0read.h"
 #include "buf0lru.h"
+#include "ha_prototypes.h"
 
 /* Maximum number of rows to prefetch; MySQL interface has another parameter */
 #define SEL_MAX_N_PREFETCH	16
@@ -3578,20 +3579,12 @@ shortcut_fails_too_big_rec:
 	if (trx->isolation_level <= TRX_ISO_READ_COMMITTED
 	    && prebuilt->select_lock_type != LOCK_NONE
 	    && trx->mysql_thd != NULL
-	    && trx->mysql_query_str != NULL
-	    && *trx->mysql_query_str != NULL) {
-
-		/* Scan the MySQL query string; check if SELECT is the first
-		word there */
-
-		if (dict_str_starts_with_keyword(
-			    trx->mysql_thd, *trx->mysql_query_str, "SELECT")) {
+	    && thd_is_select(trx->mysql_thd)) {
 		/* It is a plain locking SELECT and the isolation
 		level is low: do not lock gaps */
 
 		set_also_gap_locks = FALSE;
 	}
-	}
 
 	/* Note that if the search mode was GE or G, then the cursor
 	naturally moves upward (in fetch next) in alphabetical order,