Fix incorrect initialization of BackendActivityBuffer.

Since commit c8e8b5a6e, this has been zeroed out using the wrong length.
In practice the length would always be too small, leading to not zeroing
the whole buffer rather than clobbering additional memory; and that's
pretty harmless, both because shmem would likely start out as zeroes
and because we'd reinitialize any given entry before use.  Still,
it's bogus, so fix it.

Reported by Petru-Florin Mihancea (bug #15312)

Discussion: https://postgr.es/m/153363913073.1303.6518849192351268091@wrigleys.postgresql.org

diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index a121e7fdcd3c97d40c4da76d1483dfcd0a62df5f..50960f738e4a672e56029d2b9d94143279e2e3b3 100644 (file)
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -2695,7 +2695,7 @@ CreateSharedBackendStatus(void)
 
    if (!found)
    {
-       MemSet(BackendActivityBuffer, 0, size);
+       MemSet(BackendActivityBuffer, 0, BackendActivityBufferSize);
 
        /* Initialize st_activity pointers. */
        buffer = BackendActivityBuffer;