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View is not using a table index

From: Dan Shea <dan(dot)shea(at)ec(dot)gc(dot)ca>
To: <pgsql-performance(at)postgresql(dot)org>
Subject: View is not using a table index
Date: 2007-04-24 15:17:14
Message-ID: 75312DFA648AF74D8A236E5269BFBE4B04292F00@ncrx3.ncr.int.ec.gc.ca (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-performance
We have a table which we want to normalize and use the same SQL to
perform selects using a view.  
The old table had 3 columns in it's index
(region_id,wx_element,valid_time). 
The new table meteocode_elmts has a similar index but the region_id is a
reference to another table region_lookup and wx_element to table
meteocode_elmts_lookup.  This will make our index and table
significantly smaller.  
As stated ablove we want to use the same SQL query to check the view.  
The problem is we have not been able to set up the view so that it
references the "rev" index.  It just uses the region_id but ignores the
wx_element, therefore the valid_time is also ignored.  The rev index now
consists of region_id(reference to  region_lookup
table),wx_element(reference to meteocode_elmts_lookup) and valid_time.

We are using Postgresql 7.4.0.  Below is the relevant views and tables
plus an explain analyze of the query to the old table and the view.

Old table forceastelement
phoenix=# \d forecastelement 
              Table "public.forecastelement" 
     Column     |            Type             | Modifiers 
----------------+-----------------------------+-----------
 origin         | character varying(10)       | not null 
 timezone       | character varying(99)       | not null 
 region_id      | character varying(20)       | not null 
 wx_element     | character varying(99)       | not null 
 value          | character varying(99)       | not null 
 flag           | character(3)                | not null 
 units          | character varying(99)       | not null 
 valid_time     | timestamp without time zone | not null 
 issue_time     | timestamp without time zone | not null 
 next_forecast  | timestamp without time zone | not null  reception_time
| timestamp without time zone | not null
Indexes: 
    "forecastelement_rwv_idx" btree (region_id, wx_element, valid_time) 

New and view nad tables are
phoenix=# \d fcstelmt_view 
               View "public.fcstelmt_view" 
     Column     |            Type             | Modifiers 
----------------+-----------------------------+-----------
 origin         | character varying(10)       | 
 timezone       | character varying(10)       | 
 region_id      | character varying(99)       | 
 wx_element     | character varying(99)       | 
 value          | character varying(99)       | 
 flag           | character(3)                | 
 unit           | character varying           | 
 valid_time     | timestamp without time zone | 
 issue_time     | timestamp without time zone | 
 next_forecast  | timestamp without time zone |  reception_time |
timestamp without time zone | 

View definition: 
 SELECT meteocode_bltns.origin, meteocode_bltns.timezone,
region_lookup.region_id, meteocode_elmts_lookup.wx_element,
meteocode_elmts.value, meteocode_bltns.flag, ( SELECT
meteocode_units_lookup.unit FROM meteocode_units_lookup WHERE
meteocode_units_lookup.id = meteocode_elmts.unit_id) AS unit,
meteocode_elmts.valid_time, meteocode_bltns.issue_time,
meteocode_bltns.next_forecast, meteocode_bltns.reception_time FROM
meteocode_bltns, meteocode_elmts, region_lookup, meteocode_elmts_lookup
WHERE meteocode_bltns.meteocode_id = meteocode_elmts.meteocode AND
region_lookup.id = meteocode_elmts.reg_id AND meteocode_elmts_lookup.id
= meteocode_elmts.wx_element_id;

phoenix=# \d meteocode_elmts 
             Table "public.meteocode_elmts" 
    Column     |            Type             | Modifiers 
---------------+-----------------------------+-----------
 meteocode     | integer                     | 
 value         | character varying(99)       | not null 
 unit_id       | integer                     | 
 valid_time    | timestamp without time zone | not null 
 lcleffect     | integer                     | 
 reg_id        | integer                     | 
 wx_element_id | integer                     | 
Indexes: 
    "rev" btree (reg_id, wx_element_id, valid_time) phoenix=# \d
meteocode_bltns 
                                      Table "public.meteocode_bltns" 
     Column     |            Type             |
Modifiers 
----------------+-----------------------------+-------------------------
----------------+-----------------------------+-------------------------
----------------+-----------------------------+---------
 meteocode_id   | integer                     | not null default
nextval('"meteocode_bltns_idseq"'::text) 
 origin         | character varying(10)       | not null 
 header         | character varying(20)       | not null 
 timezone       | character varying(10)       | not null 
 flag           | character(3)                | not null 
 initial        | character varying(40)       | not null 
 issue_time     | timestamp without time zone | not null 
 next_forecast  | timestamp without time zone | not null  reception_time
| timestamp without time zone | not null
Indexes: 
    "meteocode_bltns_meteocode_id_idx" btree (meteocode_id) 

phoenix=# \d region_lookup 
         Table "public.region_lookup" 
  Column   |         Type          | Modifiers 
-----------+-----------------------+-----------
 id        | integer               | not null 
 region_id | character varying(99) |
Indexes: 
    "region_lookup_pkey" primary key, btree (id) 

phoenix=# \d meteocode_elmts_lookup 
     Table "public.meteocode_elmts_lookup" 
   Column   |         Type          | Modifiers 
------------+-----------------------+-----------
 id         | integer               | not null 
 wx_element | character varying(99) | not null
Indexes: 
    "meteocode_elmts_lookup_pkey" primary key, btree (id) 
    "wx_element_idx" btree (wx_element) 

phoenix=# \d meteocode_units_lookup 
   Table "public.meteocode_units_lookup" 
 Column |         Type          | Modifiers 
--------+-----------------------+-----------
 id     | integer               | not null 
 unit   | character varying(99) | not null 
Indexes: 
    "meteocode_units_lookup_pkey" primary key, btree (id) 

VIEW 
PWFPM_DEV=# explain analyze SELECT
origin,timezone,region_id,wx_element,value,flag,unit,valid_time,issue_ti
me,next_forecast FROM fcstelmt_view where origin = 'OFFICIAL' and
timezone = 'CST6CDT' and region_id = 'PU-REG-WNT-00027' and wx_element
= 'NGTPERIOD_MINTEMP' and value = '-26' and flag= 'REG' and unit =
'CELSIUS' and valid_time = '2007-04-09 00:00:00'  and     issue_time =
'2007-04-08 15:00:00' and next_forecast = '2007-04-09 04:00:00' ;
QUERY PLAN

 Hash Join  (cost=1.47..1309504.33 rows=1 width=264) (actual
time=21.609..84.940 rows=1 loops=1) 
   Hash Cond: ("outer".wx_element = "inner".id) 
   ->  Nested Loop  (cost=0.00..1309501.76 rows=1 width=201) (actual
time=17.161..80.489 rows=1 loops=1) 
         ->  Nested Loop  (cost=0.00..1309358.57 rows=1 width=154)
(actual time=17.018..80.373 rows=2 loops=1) 
               ->  Seq Scan on region_lookup  (cost=0.00..26.73 rows=7
width=71) (actual time=0.578..2.135 rows=1 loops=1) 
  Filter: ((region_id)::text = 'PU-REG-WNT-00027'::text) 
               ->  Index Scan using rev on meteocode_elmts
(cost=0.00..187047.39 rows=1 width=91) (actual time=16.421..78    .208
rows=2 loops=1) 
 Index Cond: ("outer".id = meteocode_elmts.region_id) 
  Filter: (((value)::text = '-26'::text) AND (valid_time = '2007-04-09
00:00:00'::timestamp without tim    e zone) AND (((subplan))::text =
'CELSIUS'::text))
             SubPlan ->  Seq Scan on meteocode_units_lookup
(cost=0.00..1.09 rows=1 width=67) (actual time=0.013..0.018     rows=1
loops=2)
            Filter: (id = $0) 
         ->  Index Scan using meteocode_bltns_meteocode_id_idx on
meteocode_bltns  (cost=0.00..143.18 rows=1 width=55) (ac    tual
time=0.044..0.045 rows=0 loops=2)
            Index Cond: (meteocode_bltns.meteocode_id =
"outer".meteocode) 
            Filter: (((origin)::text = 'OFFICIAL'::text) AND
((timezone)::text = 'CST6CDT'::text) AND (flag = 'REG'::bp    char) AND
(issue_time = '2007-04-08 15:00:00'::timestamp without time zone) AND
(next_forecast = '2007-04-09 04:00:00'::ti    mestamp without time
zone))

   ->  Hash  (cost=1.46..1.46 rows=2 width=71) (actual time=0.081..0.081
rows=0 loops=1) 
         ->  Seq Scan on meteocode_elmts_lookup  (cost=0.00..1.46 rows=2
width=71) (actual time=0.042..0.076 rows=1 loops=    1)
               Filter: ((wx_element)::text = 'NGTPERIOD_MINTEMP'::text) 
   SubPlan 
     ->  Seq Scan on meteocode_units_lookup  (cost=0.00..1.09 rows=1
width=67) (actual time=0.007..0.012 rows=1 loops=1)
           Filter: (id = $0)
 Total runtime: 85.190 ms
(22 rows) 

OLD TABLE 
PWFPM_DEV=# explain analyze SELECT
origin,timezone,region_id,wx_element,value,flag,units,valid_time,issue_t
ime,next_forecast FROM forecastelement where origin = 'OFFICIAL' and
timezone = 'CST6CDT' and region_id = 'PU-REG-WNT-00027' and wx_element =
'NGTPERIOD_MINTEMP' and value = '-26' and flag= 'REG' and units =
'CELSIUS' and valid_time = '2007-04-09 00:00:00'  and issue_time =
'2007-04-08 15:00:00' and next_forecast = '2007-04-09 04:00:00' ;
QUERY PLAN

 Index Scan using forecastelement_rwv_idx on forecastelement
(cost=0.00..4.03 rows=1 width=106) (actual time=0.207..0.207 rows=0
loops=1)
Index Cond: (((region_id)::text = 'PU-REG-WNT-00027'::text) AND
((wx_element)::text = 'NGTPERIOD_MINTEMP'::text) AND (valid_time =
'2007-04-09 00:00:00'::timestamp without time zone))
 Filter: (((origin)::text = 'OFFICIAL'::text) AND ((timezone)::text =
'CST6CDT'::text) AND ((value)::text = '-26'::text) AND (flag =
'REG'::bpchar) AND ((units)::text = 'CELSIUS'::text) AND (issue_time =
'2007-04-08 15:00:00'::timestamp without time zone) AND (next_forecast =
'2007-04-09 04:00:00'::timestamp without time zone))
 Total runtime: 0.327 ms 
(4 rows) 

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