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sysadmin:postgresql [2014/11/05 15:34] – titolo ferodasysadmin:postgresql [2015/02/12 09:01] – Indice su espressione feroda
Line 71: Line 71:
     * [4] = ... indici usati ma non efficaci     * [4] = ... indici usati ma non efficaci
     * [5] = ... tabelle vuote     * [5] = ... tabelle vuote
 +
 +====== CREAZIONE E USO INDICI =======
 +
 +  postgres# \d+ acs_service.connection_session;
 +     Column   |           Type           |                                  Modifiers                                  | Storage |                                                   Description                                                    
 +  ------------+--------------------------+-----------------------------------------------------------------------------+---------+------------------------------------------------------------------------------------------------------------------
 +   id         | integer                  | not null default nextval('acs_service.connection_session_id_seq'::regclass) | plain   | 
 +   start_time | timestamp with time zone | not null                                                                    | plain   | Moment in which the VPN session started. Obtained from $time_unix OpenVPN's envvar.
 +   duration   | interval                 |                                                                             | plain   | Duration of the connection, value is NULL until connection drops. Obtained from $time_duration OpenVPN's envvar.
 +   id_chamber | integer                  | not null                                                                    | plain   | Id of the Chamber related to the connection.
 +  Indexes:
 +    "pk_id" PRIMARY KEY, btree (id)
 +    "connection_session_duration_idx" btree (duration)
 +    "connection_session_id_chamber_idx" btree (id_chamber)
 +  Foreign-key constraints:
 +    "fk_chamber" FOREIGN KEY (id_chamber) REFERENCES acs_service.chamber(id)
 +  Has OIDs: no
 +
 +  postgres# REINDEX TABLE "acs_service"."connection_session";
 +  REINDEX
 +  postgres# EXPLAIN ANALYZE SELECT bcs.id, bcs.duration FROM acs_service.connection_session bcs WHERE bcs.duration IS NULL;
 +                                                                QUERY PLAN                                                                
 +  ------------------------------------------------------------------------------------------------------------------------------------------
 +  Bitmap Heap Scan on connection_session bcs  (cost=4.82..234.49 rows=70 width=20) (actual time=0.117..0.180 rows=67 loops=1)
 +   Recheck Cond: (duration IS NULL)
 +   ->  Bitmap Index Scan on connection_session_duration_idx  (cost=0.00..4.80 rows=70 width=0) (actual time=0.106..0.106 rows=67 loops=1)
 +         Index Cond: (duration IS NULL)
 +  Total runtime: 0.208 ms (5 rows)
 +
 +  postgres=# EXPLAIN ANALYZE SELECT bcs.id, bcs.duration FROM acs_service.connection_session bcs WHERE bcs.duration IS NOT NULL;
 +                                                          QUERY PLAN                                                           
 +  -------------------------------------------------------------------------------------------------------------------------------
 +   Seq Scan on connection_session bcs  (cost=0.00..2829.78 rows=149208 width=20) (actual time=0.008..36.858 rows=149211 loops=1)
 +   Filter: (duration IS NOT NULL)
 +  Total runtime: 46.523 ms (3 rows)
 +  
 +===== Se creo indice sull'espressione "duration IS NOT NULL" cosa succede? =====
 +
 +Niente .... :(
 +
 +    postgres=# CREATE INDEX ON "acs_service".connection_session ((duration IS NOT NULL));
 +    CREATE INDEX
 +    postgres=# REINDEX TABLE "acs_service"."connection_session";
 +    REINDEX
 +    postgres=# EXPLAIN ANALYZE SELECT bcs.id, bcs.duration FROM acs_service.connection_session bcs WHERE bcs.duration IS NOT NULL;
 +                                                              QUERY PLAN                                                       
 +    -------------------------------------------------------------------------------------------------------------------------------
 +     Seq Scan on connection_session bcs  (cost=0.00..2829.90 rows=149220 width=20) (actual time=0.011..38.323 rows=149226 loops=1)
 +       Filter: (duration IS NOT NULL)
 +     Total runtime: 48.491 ms
 +    (3 rows)
 +
 +    postgres=# EXPLAIN ANALYZE SELECT bcs.id, bcs.duration FROM acs_service.connection_session bcs WHERE bcs.duration IS NULL;         
 +                                                                    QUERY PLAN                                                            
 +    ------------------------------------------------------------------------------------------------------------------------------------------
 +     Bitmap Heap Scan on connection_session bcs  (cost=4.82..234.49 rows=70 width=20) (actual time=0.061..0.119 rows=65 loops=1)
 +       Recheck Cond: (duration IS NULL)
 +       ->  Bitmap Index Scan on connection_session_duration_idx  (cost=0.00..4.80 rows=70 width=0) (actual time=0.050..0.050 rows=66 loops=1)
 +             Index Cond: (duration IS NULL)
 +     Total runtime: 0.148 ms
 +    (5 rows)
 +
 +
 +====== Occupazione disco ======
 +
 +===== Database =====
 +
 +Lo restituisce pure in formato carino :)
 +
 +# select (pg_database_size(current_database())/(1024*1024))::text || ' MB' as db_size;
 +
 +===== Tabelle =====
 +
 +Restituisce un elenco ordinato in modo discendente di:
 +
 +  * schema (aka "directory")
 +  * tabella
 +  * occupazione su disco
 +  * occupazione totale compresi indici
 +  * numero stimato di righe
 +
 +    SELECT table_schema, table_name, 
 +      (size/1024)::varchar || ' kB' as size,
 +      (total_size/1024)::varchar || ' kB' as total_size,
 +      (CASE WHEN pg_class.reltuples > 0 THEN
 +          basic_infos.size/(8192*relpages*reltuples)
 +          ELSE 0
 +          END
 +      )::bigint AS estimated_row_count
 +      FROM (
 +        SELECT table_schema, table_name, 
 +            pg_relation_size('"' || table_schema || '"."' || table_name || '"') as size,
 +            pg_total_relation_size('"' || table_schema || '"."' || table_name || '"') as total_size
 +            FROM information_schema.tables 
 +            WHERE table_schema NOT IN ('information_schema', 'pg_catalog') 
 +        ORDER BY size DESC, total_size DESC
 +    ) AS basic_infos 
 +        JOIN pg_class
 +        ON ('"' || table_schema || '"."' || table_name || '"')::regclass = pg_class.oid
 +
 +Questa query funziona su PostgreSQL 8.4. E credo valga anche per PostgreSQL >= 9.0. Potrebbe essere interessante pubblicarla da qualche parte.
 +
 +
 +====== Informazioni varie... ======
  
 ===== Query comode x debug ===== ===== Query comode x debug =====