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 12ca29542241b2019f031ea1e3c5ff19cf7ad306..29d986a65a16473629b4762e736944ce4f886aa9 100644 (file)
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -2560,7 +2560,7 @@ pgstat_beshutdown_hook(int code, Datum arg)
  * pgstat_report_activity() -
  *
  * Called from tcop/postgres.c to report what the backend is actually doing
- * (usually "" 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
@@ -2580,29 +2580,32 @@ 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)
@@ -2610,6 +2613,7 @@ 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 e6ec37296e57e2fa1978ce8d67fd9095cb4383d6..8c1a76728defbd20d030bf917489a0d87ac2c594 100644 (file)
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -666,15 +666,8 @@ 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)