# HG changeset patch
# User Oleksandr Gavenko <gavenkoa@gmail.com>
# Date 1546383545 -7200
# Node ID 24ffd84a171c13ef84c99416a0c4b9dd109613f0
# Parent  1b3ff9b88a1263c96c0ab4283e2d07a02b418c33
MVCC and transaction id.

diff -r 1b3ff9b88a12 -r 24ffd84a171c postgres.rst
--- a/postgres.rst	Wed Jan 02 00:55:00 2019 +0200
+++ b/postgres.rst	Wed Jan 02 00:59:05 2019 +0200
@@ -119,7 +119,6 @@
 
   \dy
 
-
 List misc info::
 
   select current_database();
@@ -167,6 +166,15 @@
 
   SELECT relname, relpages FROM pg_class ORDER BY relpages DESC;
 
+MVCC and transaction id
+=======================
+
+As being MVCC Postgres doesn't delete or update existing rows. Row visibility is controled by
+transaction id (monotonous incremented number): ``xmin`` - first transaction that can see row,
+``xmax`` - last transaction that can see row:::
+
+  SELECT xmin, xmax, * FROM foo WHERE id < 5 ORDER BY id;
+
 Using psql client
 =================