From fb7ed3889fa6fc0f4aa6718ffb6574801ad12484 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 | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 44ccd37e998..688eea12a93 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -633,15 +633,13 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
{
/* Get specific pid slot */
local_beentry = pgstat_fetch_stat_local_beentry(*(int *) (funcctx->user_fctx));
- beentry = &local_beentry->backendStatus;
}
else
{
/* Get the next one in the list */
local_beentry = pgstat_fetch_stat_local_beentry(funcctx->call_cntr + 1); /* 1-based index */
- beentry = &local_beentry->backendStatus;
}
- if (!beentry)
+ if (!local_beentry)
{
int i;
@@ -655,6 +653,8 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
SRF_RETURN_NEXT(funcctx, HeapTupleGetDatum(tuple));
}
+ beentry = &local_beentry->backendStatus;
+
/* Values available to all callers */
values[0] = ObjectIdGetDatum(beentry->st_databaseid);
values[1] = Int32GetDatum(beentry->st_procpid);