Memory "leak" on every update

[tserr]

We observed, that every update on a row of a temporal enables tables leads to ~15KB additional memory usage of the processes for a connection.

Our researches showed that this memory usage is caused by lookup_versioning_hash_entry because already created entries are not found.

Steps we did to analyse:

• Debugging showed, that all calls of function "lookup_versioning_hash_entry" entered block “if (!*found)”, even the second call in a row for the same table.
• Uncommenting “memset” command showed:
  • All fields of “entry” (except relid) are 0/NULL.
  • Without "memset" all non first calls of function "lookup_versioning_hash_entry" skipped block “if (!*found)” (as intended).
  • Memory usage was constant (wanted behaviour)
• Reactivating “memset” command and subsequent setting entry->relid = relid;
  • Same behaviour as seen with uncommenting “memset” (s. above).

We don't really understand

• why the first call of “hash_search” for a table returns an initialized struct “entry” with "relid" set and all other fields filled with null values.
• why setting "entry->relid" to null leads to not finding the entry on subsequent calls of “hash_search”.

But ensuring "entry->relid" is set after the "memset" solves the issue for us.

diff --git a/versioning.c b/versioning.c
index 2497c2f..0599530 100644
--- a/versioning.c
+++ b/versioning.c
@@ -1080,6 +1080,7 @@ lookup_versioning_hash_entry(Oid relid,
        if (!*found)
        {
                memset(entry, 0, sizeof(VersioningHashEntry));
+               entry->relid = relid;

                /* Mark a newly created entry invalid. */
                entry->natts = -1;

[arkhipov]

Could you please check if the current version works for you?

[tserr]

Thanks for the fast support. The current version fixes this issue for us.