From ddc889317912fd8b654439701195a43cecfd4e79 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 10 Sep 2016 13:49:04 -0400
Subject: [PATCH] Fix miserable coding in pg_stat_get_activity().
Commit dd1a3bccc replaced a test on whether a subroutine returned a
null pointer with a test on whether &pointer->backendStatus was null.
This accidentally failed to fail, at least on common compilers, because
backendStatus is the first field in the struct; but it was surely trouble
waiting to happen. Commit f91feba87 then messed things up further,
changing the logic to
local_beentry = pgstat_fetch_stat_local_beentry(curr_backend);
if (!local_beentry)
continue;
beentry = &local_beentry->backendStatus;
if (!beentry)
{
where the second "if" is now dead code, so that the intended behavior of
printing a row with "<backend information not available>" cannot occur.
I suspect this is all moot because pgstat_fetch_stat_local_beentry
will never actually return null in this function's usage, but it's still
very poor coding. Repair back to 9.4 where the original problem was
introduced.
---
src/backend/utils/adt/pgstatfuncs.c | 26 +++++++++++---------------
1 file changed, 11 insertions(+), 15 deletions(-)
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 5d1ccf51d41..2d3cf9e4688 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -688,27 +688,17 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
MemSet(values, 0, sizeof(values));
MemSet(nulls, 0, sizeof(nulls));
- if (pid != -1)
- {
- /* Skip any which are not the one we're looking for. */
- PgBackendStatus *be = pgstat_fetch_stat_beentry(curr_backend);
-
- if (!be || be->st_procpid != pid)
- continue;
-
- }
-
/* Get the next one in the list */
local_beentry = pgstat_fetch_stat_local_beentry(curr_backend);
if (!local_beentry)
- continue;
-
- beentry = &local_beentry->backendStatus;
- if (!beentry)
{
int i;
- for (i = 0; i < sizeof(nulls) / sizeof(nulls[0]); i++)
+ /* Ignore missing entries if looking for specific PID */
+ if (pid != -1)
+ continue;
+
+ for (i = 0; i < lengthof(nulls); i++)
nulls[i] = true;
nulls[5] = false;
@@ -718,6 +708,12 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
continue;
}
+ beentry = &local_beentry->backendStatus;
+
+ /* If looking for specific PID, ignore all the others */
+ if (pid != -1 && beentry->st_procpid != pid)
+ continue;
+
/* Values available to all callers */
values[0] = ObjectIdGetDatum(beentry->st_databaseid);
values[1] = Int32GetDatum(beentry->st_procpid);
--
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