also check IsTransactionState, it helps support of pg_reload_config

[plantuner.git] / README.plantuner

diff --git a/README.plantuner b/README.plantuner
index 16aef5e..6b16fba 100644 (file)
--- a/README.plantuner
+++ b/README.plantuner
@@ -1,30 +1,52 @@
 Plantuner - enable planner hints
 
-contrib/plantuner is a contribution module for PostgreSQL 8.4+, which enable 
-planner hints.
+   contrib/plantuner is a contribution module for PostgreSQL 8.4+, which
+   enable planner hints.
 
-All work was done by Teodor Sigaev (teodor@sigaev.ru) and 
- Oleg Bartunov (oleg@sai.msu.su).
+   All work was done by Teodor Sigaev (teodor@sigaev.ru) and Oleg Bartunov
+   (oleg@sai.msu.su).
+
+   Sponsor: Nomao project (http://www.nomao.com)
 
-Sponsor: JFG Networks (www.jfg-networks.net)
 Motivation
 
-It's very interesting to be able to control planner (provide hints), which is 
-currently impossible. This first version of plantuner provides a possibility to
-hide specified indexes from PostgreSQL planner, so it will not use them.
+   Whether somebody think it's bad or not, but sometime it's very
+   interesting to be able to control planner (provide hints, which tells
+   optimizer to ignore its algorithm in part), which is currently
+   impossible in POstgreSQL. Oracle, for example, has over 120 hints, SQL
+   Server also provides hints.
+
+   This first version of plantuner provides a possibility to hide
+   specified indexes from PostgreSQL planner, so it will not use them.
+
+   There are many situation, when developer want to temporarily disable
+   specific index(es), without dropping them, or to instruct planner to
+   use specific index.
+
+   Next, for some workload PostgreSQL could be too pessimistic for
+   newly created tables and assumes much more rows in table than
+   it actually has. If plantuner.fix_empty_table GUC variable is set
+   to true then module will set to zero number of pages/tuples of
+   table which hasn't blocks in file.
 
-There are many situation, when developer want to temporarily disable specific 
-index(es), without dropping them, or to instruct planner to use specific index.
 Installation
 
-    * Get latest source of plantuner from CVS Repository
-    * gmake && gmake install && gmake installcheck
+     * Get latest source of plantuner from CVS Repository
+     * gmake && gmake install && gmake installcheck
 
-Usage
+Syntax
+       plantuner.forbid_index (deprecated)
+       plantuner.disable_index
+               List of indexes invisible to planner
+       plantuner.enable_index
+               List of indexes visible to planner even they are hided
+               by plantuner.disable_index. 
 
-To enable the module you can either load shared library 'plantuner' in psql 
-session or specify 'shared_preload_libraries' option in postgresql.conf.
+Usage
 
+   To enable the module you can either load shared library 'plantuner' in
+   psql session or specify 'shared_preload_libraries' option in
+   postgresql.conf.
 =# LOAD 'plantuner';
 =# create table test(id int);
 =# create index id_idx on test(id);
@@ -46,7 +68,7 @@ Indexes:
          Index Cond: (id = 1)
 (4 rows)
 =# set enable_seqscan=off;
-=# set plantuner.forbid_index='id_idx2';
+=# set plantuner.disable_index='id_idx2';
 =# explain select id from test where id=1;
                               QUERY PLAN
 ----------------------------------------------------------------------
@@ -55,11 +77,20 @@ Indexes:
    ->  Bitmap Index Scan on id_idx  (cost=0.00..4.34 rows=12 width=0)
          Index Cond: (id = 1)
 (4 rows)
-=# set plantuner.forbid_index='id_idx2,id_idx';
+=# set plantuner.disable_index='id_idx2,id_idx';
 =# explain select id from test where id=1;
                                QUERY PLAN
 -------------------------------------------------------------------------
  Seq Scan on test  (cost=10000000000.00..10000000040.00 rows=12 width=4)
    Filter: (id = 1)
 (2 rows)
+=# set plantuner.enable_index='id_idx';
+=# explain select id from test where id=1;
+                              QUERY PLAN
+-----------------------------------------------------------------------
+ Bitmap Heap Scan on test  (cost=4.34..15.03 rows=12 width=4)
+   Recheck Cond: (id = 1)
+   ->  Bitmap Index Scan on id_idx  (cost=0.00..4.34 rows=12 width=0)
+         Index Cond: (id = 1)
+(4 rows)