Hi Hackers,
I noticed a memory leak:
```
static void
libpqrcv_processTuples(PGresult *pgres, WalRcvExecResult *walres,
const int nRetTypes, const Oid
*retTypes)
{
walres->tuplestore = tuplestore_begin_heap(true, false, work_mem);
/* Create tuple descriptor corresponding to expected result. */
walres->tupledesc = CreateTemplateTupleDesc(nRetTypes);
for (coln = 0; coln < nRetTypes; coln++)
TupleDescInitEntry(walres->tupledesc, (AttrNumber) coln + 1,
PQfname(pgres, coln),
retTypes[coln], -1, 0);
attinmeta = TupleDescGetAttInMetadata(walres->tupledesc); <== attinmeta
is not free-ed
/* No point in doing more here if there were no tuples returned. */
if (PQntuples(pgres) == 0)
return;
```
I understand that it is a common pattern where memory are free-ed automatically
by destroying memory context. However, when I analyzed the usage of
libpqrcv_processTuples(), I feel it is a memory leak.
A typical call model is like:
```
Caller of walrcv_exec() {
WalRcvExecResult *res; # define a local variable to store result
res = walrcv_exec(…); # walrcv_exec will return a result
-> walrcv_exec(…) {
WalRcvExecResult *walres = palloc0_object(WalRcvExecResult); #
allocate memory for result
walres->status = WALRCV_OK_TUPLES;
libpqrcv_processTuples(pgres, walres, nRetTypes, retTypes); #
libpqrcv_processTuples will fill in result
-> libpqrcv_processTuples(… walres …) {
walres->tuplestore = tuplestore_begin_heap() # allocate
memory for tuplestore
walres->tupledesc = CreateTemplateTupleDesc(nRetTypes); #
allocate memory for tupledesc
attinmeta = TupleDescGetAttInMetadata(walres->tupledesc); #
allocate memory for attinmeta
}
return walres;
}
walrcv_clear_result(res); # free res object, nested tuplestore and
tupledesc are free-ed as well, but attinmeta is leaked
}
```
We can see that, the result object is explicitly free-ed by
walrcv_clear_result. But the memory pointed by attinmeta is leaked, it will
only be free-ed when the corresponding memory context is destroyed.
As walrcv_exec() is widely called in a lot of places, it’s hard to tell in
which memory context libpqrcv_processTuples() runs, so I think attinmeta should
be free-ed.
But I then noticed that, attinmeta is created by TupleDescGetAttInMetadata()
that allocates an AttInMetadata object itself as well as several nested
objects, and there is not a function to deeply free attinmeta, thus a simple
pfree(attinmeta) won’t resolve the leak problem. Does that mean we
intentionally to not want to free memory of AttInMetadata?
So, rather than posting a patch directly, I’d like to confirm with folks who
are familiar with this area. Is this a real memory leak worthing a fix?
Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/
