doc: Fix explanation related to pg_shmem_allocations

Offsets are shown as NULL only for anonymous allocations.

Author: Benoit Lobréau
Reviewed-by: Kyotaro Horiguchi
Discussion: https://postgr.es/m/CAPE8EZ5Lnoyqoz7aZpvQM0E8sW+hw+k6G2NULe+m4arFRrA1aA@mail.gmail.com
Backpatch-through: 13

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index c6500b47047c05af49d1ef77a1f1fc6f89a54fec..70536ce5c74461ef1c61d9e7c4c811149dfea003 100644 (file)
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -12305,7 +12305,7 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
       </para>
       <para>
        The offset at which the allocation starts. NULL for anonymous
-       allocations and unused memory.
+       allocations, since details related to them are not known.
       </para></entry>
      </row>