Avoid updating our PgBackendStatus entry when track_activities is off.

The point of turning off track_activities is to avoid this reporting
overhead, but a thinko in commit 4f42b546fd87a80be30c53a0f2c897acb826ad52
caused pgstat_report_activity() to perform half of its updates anyway.
Fix that, and also make sure that we clear all the now-disabled fields
when transitioning to the non-reporting state.

diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index f890e2bc66336aa7c9238ed2ec7d91fef1e0d200..edad1401e452d8f4821b1ab2a6213ddf567d310c 100644 (file)
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -2520,7 +2520,7 @@ pgstat_beshutdown_hook(int code, Datum arg)
  * pgstat_report_activity() -
  *
  *     Called from tcop/postgres.c to report what the backend is actually doing
- *     (usually "<IDLE>" or the start of the query to be executed).
+ *     (but note cmd_str can be NULL for certain cases).
  *
  * All updates of the status entry follow the protocol of bumping
  * st_changecount before and after.  We use a volatile pointer here to
@@ -2540,29 +2540,32 @@ pgstat_report_activity(BackendState state, const char *cmd_str)
        if (!beentry)
                return;
 
-       /*
-        * To minimize the time spent modifying the entry, fetch all the needed
-        * data first.
-        */
-       current_timestamp = GetCurrentTimestamp();
-
-       if (!pgstat_track_activities && beentry->st_state != STATE_DISABLED)
+       if (!pgstat_track_activities)
        {
-               /*
-                * Track activities is disabled, but we have a non-disabled state set.
-                * That means the status changed - so as our last update, tell the
-                * collector that we disabled it and will no longer update.
-                */
-               beentry->st_changecount++;
-               beentry->st_state = STATE_DISABLED;
-               beentry->st_state_start_timestamp = current_timestamp;
-               beentry->st_changecount++;
-               Assert((beentry->st_changecount & 1) == 0);
+               if (beentry->st_state != STATE_DISABLED)
+               {
+                       /*
+                        * track_activities is disabled, but we last reported a
+                        * non-disabled state.  As our final update, change the state and
+                        * clear fields we will not be updating anymore.
+                        */
+                       beentry->st_changecount++;
+                       beentry->st_state = STATE_DISABLED;
+                       beentry->st_state_start_timestamp = 0;
+                       beentry->st_activity[0] = '\0';
+                       beentry->st_activity_start_timestamp = 0;
+                       /* st_xact_start_timestamp and st_waiting are also disabled */
+                       beentry->st_xact_start_timestamp = 0;
+                       beentry->st_waiting = false;
+                       beentry->st_changecount++;
+                       Assert((beentry->st_changecount & 1) == 0);
+               }
                return;
        }
 
        /*
-        * Fetch more data before we start modifying the entry
+        * To minimize the time spent modifying the entry, fetch all the needed
+        * data first.
         */
        start_timestamp = GetCurrentStatementStartTimestamp();
        if (cmd_str != NULL)
@@ -2570,6 +2573,7 @@ pgstat_report_activity(BackendState state, const char *cmd_str)
                len = pg_mbcliplen(cmd_str, strlen(cmd_str),
                                                   pgstat_track_activity_query_size - 1);
        }
+       current_timestamp = GetCurrentTimestamp();
 
        /*
         * Now update the status entry

diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 7c0705abcc9eb355e2df71b5ec9e11e81ce9f7ec..6f2514748572c8bfd91d56d33964078136a8e8ad 100644 (file)
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -665,15 +665,8 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
                                        nulls[4] = true;
                                        break;
                        }
-                       if (beentry->st_state == STATE_UNDEFINED ||
-                               beentry->st_state == STATE_DISABLED)
-                       {
-                               values[5] = CStringGetTextDatum("");
-                       }
-                       else
-                       {
-                               values[5] = CStringGetTextDatum(beentry->st_activity);
-                       }
+
+                       values[5] = CStringGetTextDatum(beentry->st_activity);
                        values[6] = BoolGetDatum(beentry->st_waiting);
 
                        if (beentry->st_xact_start_timestamp != 0)