Deal with PostgreSQL 10 in streaming replication delay checking.

From PostgreSQL 10 or later, some built in function names which are
used in streaming replication delay checking are changed. To deal with
this, get server_version_num from backend to change the calling
functions and cache them. Using 'S' message to extract the server
version string while connecting backend could be an idea, but
unfortunately connecting function used in streaming replication delay
checking does not handle 'S' parameter. Also converting from the
server version string to the server_version_num can be backend
dependent, so to extract the server_version_num would be safer.

diff --git a/src/streaming_replication/pool_worker_child.c b/src/streaming_replication/pool_worker_child.c
index 824c0f5eb367e9b826cc2cf5c10e8f2f544b41bf..f4645ee69b61b54273fcbb846d18c10e0c292cd2 100644 (file)
--- a/src/streaming_replication/pool_worker_child.c
+++ b/src/streaming_replication/pool_worker_child.c
@@ -5,7 +5,7 @@
  * pgpool: a language independent connection pool server for PostgreSQL
  * written by Tatsuo Ishii
  *
- * Copyright (c) 2003-2014     PgPool Global Development Group
+ * Copyright (c) 2003-2017     PgPool Global Development Group
  *
  * Permission to use, copy, modify, and distribute this software and
  * its documentation for any purpose and without fee is hereby
@@ -75,6 +75,8 @@ static unsigned long long int text_to_lsn(char *text);
 static RETSIGTYPE my_signal_handler(int sig);
 static RETSIGTYPE reload_config_handler(int sig);
 static void reload_config(void);
+static int get_query_result(int backend_id, char *query, POOL_SELECT_RESULT **res);
+
 #define CHECK_REQUEST \
        do { \
                if (reload_config_request) \
@@ -88,6 +90,9 @@ static void reload_config(void);
                } \
     } while (0)
 
+
+#define PG10_SERVER_VERSION    100000  /* PostgreSQL 10 server version num */
+
 /*
 * worker child main loop
 */
@@ -157,7 +162,7 @@ void do_worker_child(void)
                 * If streaming replication mode, do time lag checking
                 */
 
-               if (pool_config->sr_check_period > 0 && MASTER_SLAVE && pool_config->master_slave_sub_mode == STREAM_MODE)
+               if (pool_config->sr_check_period > 0 && STREAM)
                {
                        establish_persistent_connection();
             PG_TRY();
@@ -229,6 +234,9 @@ static void discard_persistent_connection(void)
  */
 static void check_replication_time_lag(void)
 {
+       /* backend server version cache */
+       static int server_version[MAX_NUM_BACKENDS];
+
        int i;
        int active_nodes = 0;
        POOL_SELECT_RESULT *res;
@@ -286,50 +294,43 @@ static void check_replication_time_lag(void)
 
                }
 
-               if (PRIMARY_NODE_ID == i)
-               {
-                       query = "SELECT pg_current_xlog_location()";
-               }
-               else
+               if (server_version[i] == 0)
                {
-                       query = "SELECT pg_last_xlog_replay_location()";
-               }
+                       query = "SELECT current_setting('server_version_num')";
 
-               do_query(slots[i]->con, query, &res, PROTO_MAJOR_V3);
-
-               if (!res)
-               {
-            ereport(ERROR,
-                (errmsg("Failed to check replication time lag"),
-                     errdetail("Query to node (%d) returned no result for node",i)));
+                       /* Get backend serversion. If the query fails, keep previous info. */
+                       if (get_query_result(i, query, &res) == 0)
+                       {
+                               server_version[i] = atoi(res->data[0]);
+                               ereport(DEBUG1,
+                                               (errmsg("backend %d server version: %d", i, server_version[i])));
+                       }
+                       
                }
-               if (res->numrows <= 0)
+
+               if (PRIMARY_NODE_ID == i)
                {
-                       free_select_result(res);
-            ereport(ERROR,
-                (errmsg("Failed to check replication time lag"),
-                     errdetail("Query to node (%d) returned result with no rows",i)));
+                       if (server_version[i] >= PG10_SERVER_VERSION)
+                               query = "SELECT pg_current_wal_location()";
+                       else
+                               query = "SELECT pg_current_xlog_location()";
                }
-               if (res->data[0] == NULL)
+               else
                {
-                       free_select_result(res);
-            ereport(ERROR,
-                (errmsg("Failed to check replication time lag"),
-                     errdetail("Query to node (%d) returned no data",i)));
+                       if (server_version[i] >= PG10_SERVER_VERSION)
+                               query = "SELECT pg_last_wal_replay_location()";
+                       else
+                               query = "SELECT pg_last_xlog_replay_location()";
                }
 
-               if (res->nullflags[0] == -1)
+               if (get_query_result(i, query, &res) == 0)
                {
+                       lsn[i] = text_to_lsn(res->data[0]);
                        free_select_result(res);
-                       lsn[i] = 0;
-            ereport(ERROR,
-                (errmsg("Failed to check replication time lag"),
-                     errdetail("Query to node (%d) returned NULL data",i)));
                }
                else
                {
-                       lsn[i] = text_to_lsn(res->data[0]);
-                       free_select_result(res);
+                       lsn[i] = 0;
                }
        }
 
@@ -449,3 +450,54 @@ static void reload_config(void)
                load_hba(get_hba_file_name());
        reload_config_request = 0;
 }
+
+/*
+ * Execute query against specified backend.
+ * Return -1 on failure or 0 otherwise.
+ * Caller must prepare memory for POOL_SELECT_RESULT and pass it as "res".
+ */
+
+static         int get_query_result(int backend_id, char *query, POOL_SELECT_RESULT **res)
+{
+       int sts = -1;
+
+       do_query(slots[backend_id]->con, query, res, PROTO_MAJOR_V3);
+
+       if (!res)
+       {
+               ereport(ERROR,
+                               (errmsg("Failed to check replication time lag"),
+                                errdetail("Query to node (%d) returned no result for node", backend_id)));
+               return sts;
+       }
+
+       if ((*res)->numrows <= 0)
+       {
+               free_select_result(*res);
+               ereport(ERROR,
+                               (errmsg("Failed to check replication time lag"),
+                                errdetail("Query to node (%d) returned result with no rows", backend_id)));
+               return sts;
+       }
+
+       if ((*res)->data[0] == NULL)
+       {
+               free_select_result(*res);
+               ereport(ERROR,
+                               (errmsg("Failed to check replication time lag"),
+                                errdetail("Query to node (%d) returned no data", backend_id)));
+               return sts;
+       }
+
+       if ((*res)->nullflags[0] == -1)
+       {
+               free_select_result(*res);
+               ereport(ERROR,
+                               (errmsg("Failed to check replication time lag"),
+                                errdetail("Query to node (%d) returned NULL data", backend_id)));
+               return sts;
+       }
+
+       sts = 0;
+       return sts;
+}