Make EXPLAIN (BUFFERS) track blocks dirtied, as well as those written.

Also expose the new counters through pg_stat_statements.

Patch by me.  Review by Fujii Masao and Greg Smith.

1 files changed, 9 insertions, 3 deletions

diff --git a/doc/src/sgml/ref/explain.sgml b/doc/src/sgml/ref/explain.sgml
index 419b72cad34..1f35a1d1552 100644
--- a/doc/src/sgml/ref/explain.sgml
+++ b/doc/src/sgml/ref/explain.sgml
@@ -155,14 +155,20 @@ ROLLBACK;
     <listitem>
      <para>
       Include information on buffer usage. Specifically, include the number of
-      shared blocks hits, reads, and writes, the number of local blocks hits,
-      reads, and writes, and the number of temp blocks reads and writes.
-      A <quote>hit</> means that a read was avoided because the block was
+      shared blocks hit, read, dirtied, and written, the number of local blocks
+      hit, read, dirtied, and written, and the number of temp blocks read and
+      written.
+      A <emphasis>hit</> means that a read was avoided because the block was
       found already in cache when needed.
       Shared blocks contain data from regular tables and indexes;
       local blocks contain data from temporary tables and indexes;
       while temp blocks contain short-term working data used in sorts, hashes,
       Materialize plan nodes, and similar cases.
+      The number of blocks <emphasis>dirtied</> indicates the number of
+      previously unmodified blocks that were changed by this query; while the
+      number of blocks <emphasis>written</> indicates the number of
+      previously-dirtied blocks evicted from cache by this backend during
+      query processing.
       The number of blocks shown for an
       upper-level node includes those used by all its child nodes.  In text
       format, only non-zero values are printed.  This parameter may only be