Subject: Incorrect comment for memset() on pgssHashKey?

From: Japin Li <[email-masked]>
Date: Tue, 27 Jun 2023 12:32:10 +0800

Hi,

Commit 6b4d23feef introduces a toplevel field in pgssHashKey, which leads
padding.  In pgss_store(), it comments that memset() is required when
pgssHashKey is without padding only.

@@ -1224,9 +1227,14 @@ pgss_store(const char *query, uint64 queryId,
     query = CleanQuerytext(query, &query_location, &query_len);

     /* Set up key for hashtable search */
+
+    /* memset() is required when pgssHashKey is without padding only */
+    memset(&key, 0, sizeof(pgssHashKey));
+
     key.userid = GetUserId();
     key.dbid = MyDatabaseId;
     key.queryid = queryId;
+    key.toplevel = (exec_nested_level == 0);

     /* Lookup the hash table entry with shared lock. */
     LWLockAcquire(pgss->lock, LW_SHARED);

However, we need memset() only when pgssHashKey has padding, right?

-- 
Regrads,
Japin Li.

diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c
index 21bede29fe..f6ed87f1e6 100644
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -1257,7 +1257,7 @@ pgss_store(const char *query, uint64 queryId,
 
 	/* Set up key for hashtable search */
 
-	/* memset() is required when pgssHashKey is without padding only */
+	/* memset() is required when pgssHashKey is with padding only */
 	memset(&key, 0, sizeof(pgssHashKey));
 
 	key.userid = GetUserId();

---

From: Heikki Linnakangas <[email-masked]>
Date: Tue, 27 Jun 2023 10:18:11 +0300

> However, we need memset() only when pgssHashKey has padding, right?

Yep. I changed the comment to just "clear padding". Thanks!

-- 
Heikki Linnakangas
Neon (https://neon.tech)