Fix pg_stat_activity show wrong session id after session reset bug (#5757)

* Fix pg_stat_activity show wrong session id after session reset bug

Currently if a session is reset because of some error such as OOM,
after call CheckForResetSession, gp_session_id will bump to a new one,
but sess_id in pg_stat_activity remains unchanged and show the wrong number.
This commit changes sess_id in pg_stat_activity, once a session is reset.

* Refactor test using gp_execute_on_server to trigger session reset

src/backend/cdb/dispatcher/cdbgang.c

@@ -20,6 +20,7 @@
 
 #include "libpq-fe.h"
 #include "miscadmin.h"			/* MyDatabaseId */
+#include "pgstat.h"			/* pgstat_report_sessionid() */
 #include "storage/proc.h"		/* MyProc */
 #include "storage/ipc.h"
 #include "utils/memutils.h"
@@ -1421,6 +1422,7 @@ CheckForResetSession(void)
 
 	gp_session_id = newSessionId;
 	gp_command_count = 0;
+	pgstat_report_sessionid(newSessionId);
 
 	/* Update the slotid for our singleton reader. */
 	if (SharedLocalSnapshotSlot != NULL)

src/backend/postmaster/pgstat.c

@@ -2763,6 +2763,27 @@ gpstat_report_waiting(char reason)
 	beentry->st_waiting = reason;
 }
 
+/* ----------
+ * pgstat_report_sessionid() -
+ *
+ * 	Called from cdbgang to report a session is reset.
+ *
+ * ----------
+ */
+void
+pgstat_report_sessionid(int new_sessionid)
+{
+	volatile PgBackendStatus *beentry = MyBEEntry;
+
+	if (!beentry)
+		return;
+
+	beentry->st_changecount++;
+	beentry->st_session_id = new_sessionid;
+	beentry->st_changecount++;
+	Assert((beentry->st_changecount & 1) == 0);
+}
+
 /* ----------
  * pgstat_read_current_status() -
  *

src/include/pgstat.h

@@ -862,6 +862,7 @@ extern void pgstat_report_txn_timestamp(TimestampTz tstamp);
 extern void pgstat_report_waiting(bool waiting);
 #endif
 extern void gpstat_report_waiting(char reason);
+extern void pgstat_report_sessionid(int new_sessionid);
 
 extern void pgstat_report_activity(BackendState state, const char *cmd_str);
 extern void pgstat_report_tempfile(size_t filesize);

src/test/regress/greenplum_schedule

@@ -209,6 +209,7 @@ test: vacuum_full_heap_bitmapindex
 test: ao_checksum_corruption AOCO_Compression2 table_statistics fts_error
 test: metadata_track
 test: workfile_mgr_test
+test: session_reset
 
 test: psql_gp_commands pg_resetxlog
 

src/test/regress/input/session_reset.source

+
+set log_min_messages to ERROR;
+
+CREATE FUNCTION gp_execute_on_server(content smallint, query cstring) returns boolean
+language C as '@abs_builddir@/regress@DLSUFFIX@', 'gp_execute_on_server';
+
+-- terminate backend process for this session on segment with content ID = 0
+select gp_execute_on_server(0::smallint, 'select pg_terminate_backend(pg_backend_pid())'::cstring);
+
+-- session is reset and gp_session_id value changes
+-- sess_id in pg_stat_activity should be consistent with gp_session_id
+select session_id AS session_not_in_stat_activity from (select paramvalue AS session_id from gp_toolkit.gp_param_settings() where paramname='gp_session_id' and paramsegment = 0) right_id where right_id.session_id not in (select sess_id::text from pg_stat_activity);
+
+set log_min_messages to default;

src/test/regress/output/session_reset.source

+set log_min_messages to ERROR;
+CREATE FUNCTION gp_execute_on_server(content smallint, query cstring) returns boolean
+language C as '@abs_builddir@/regress@DLSUFFIX@', 'gp_execute_on_server';
+-- terminate backend process for this session on segment with content ID = 0
+select gp_execute_on_server(0::smallint, 'select pg_terminate_backend(pg_backend_pid())'::cstring);
+ERROR:  terminating connection due to administrator command  (seg0 10.152.10.149:25432 pid=32665)
+-- session is reset and gp_session_id value changes
+-- sess_id in pg_stat_activity should be consistent with gp_session_id
+select session_id AS session_not_in_stat_activity from (select paramvalue AS session_id from gp_toolkit.gp_param_settings() where paramname='gp_session_id' and paramsegment = 0) right_id where right_id.session_id not in (select sess_id::text from pg_stat_activity);
+ session_not_in_stat_activity 
+------------------------------
+(0 rows)
+
+set log_min_messages to default;

src/test/regress/sql/.gitignore

@@ -43,3 +43,4 @@ gp_tablespace.sql
 partition_ddl.sql
 autovacuum-template0.sql
 rpt_tpch.sql
+session_reset.sql