doc: clarify the effect of concurrent work_mem allocations

Reported-by: Sami Imseih
Discussion: https://postgr.es/m/66590882-F48C-4A25-83E3-73792CF8C51F@amazon.com

Backpatch-through: 11

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 7311169bddeecd72ba3b5c54bf51572cf2e110e7..42877654cd69c423cda5614f08562e2f6f25bdf6 100644 (file)
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1697,9 +1697,10 @@ include_dir 'conf.d'
         (such as a sort or hash table) before writing to temporary disk files.
         If this value is specified without units, it is taken as kilobytes.
         The default value is four megabytes (<literal>4MB</literal>).
-        Note that for a complex query, several sort or hash operations might be
-        running in parallel; each operation will be allowed to use as much memory
-        as this value specifies before it starts to write data into temporary
+        Note that a complex query might perform several sort and hash
+        operations at the same time, with each operation generally being
+        allowed to use as much memory as this value specifies before it
+        starts to write data into temporary
         files. Also, several running sessions could be doing such operations
         concurrently.  Therefore, the total memory used could be many
         times the value of <varname>work_mem</varname>; it is necessary to