Hi Martin,
it seems that the snap_time condition can not be pushed down into the better
view.
Probably the window function is preventing that. You might want to experiment
based on that.
(https://asktom.oracle.com/pls/apex/f?p=100:11:0::NO::P11_QUESTION_ID:3469884600671).
It should be possible to push a condition based on column included in the
partition clause of wndow function.
You use trunc(SNAP_TIME) there.
Try using trunc(SNAP_TIME) everywhere or just snap_time plain.
Regards
Lothar
----Ursprüngliche Nachricht----
Von : martin.a.berger@xxxxxxxxx
Datum : 08/10/2018 - 13:58 (GMT)
An : oracle-l@xxxxxxxxxxxxx
Betreff : window function vs. PARTITION RANGE ITERATOR
Dear list,
I have a DB (12.1.0.2 - Jan 2018 BP - 2 node RAC)
with a table "SYSSTAT_METRICS" which holds regular snapshots of sysstat metrics
of many DBs.
the table has columns STAT_NAME, SNAP_TIME, DATABASE_ID, INSTANCE_NAME, SERVER,
STARTUP_TIME, VALUE.
The table is partitioned by LIST ("STAT_NAME") and subpartitioned BY RANGE
("SNAP_TIME")
The SNAP_TIME subpartitions are monthly partitions. (details at the end of this
email)
I want to have a View query which gives daily last snap_time & value for every
stat, db, instance, server. In this view I'd like to efficient filter by
STAT_NAME (most only 1 statistic of interest) and SNAP_TIME (e.g. last month or
last 3 month - or December-2017).
I have a select like this:
with raw_data as (select /*+ NO_INDEX( h ) */ h.*, h.snap_time snap_time2
from sysstat_metrics h
where 1=1
and snap_time >= sysdate - 3
), better as (
select stat_name, instance_name, database_id, server, trunc(snap_time)
trunc_snap, snap_time, value, rank()
OVER (PARTITION BY STAT_NAME, instance_name,database_id, server,
trunc(SNAP_TIME) ORDER BY SNAP_TIME desc) as rr
from raw_data)
select
-- BX011
*
from better
where rr=1
and stat_name='physical read bytes'
-- and snap_time >= sysdate - 3
;
The Plan shows
Plan hash value: 1030407344
---------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows |
A-Rows | A-Time | Buffers | Reads | OMem | 1Mem | Used-Mem |
---------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | |
2868 |00:00:00.21 | 1921 | 11 | | | |
|* 1 | VIEW | | 1 | 3 |
2868 |00:00:00.21 | 1921 | 11 | | | |
|* 2 | WINDOW SORT PUSHED RANK | | 1 | 3 |
2868 |00:00:00.21 | 1921 | 11 | 6715K| 1041K| 5968K (0)|
| 3 | PARTITION LIST SINGLE | | 1 | 3 |
51612 |00:00:00.04 | 1921 | 11 | | | |
| 4 | PARTITION RANGE ITERATOR| | 1 | 3 |
51612 |00:00:00.04 | 1921 | 11 | | | |
|* 5 | TABLE ACCESS FULL | SYSSTAT_METRICS | 4 | 3 |
51612 |00:00:00.03 | 1921 | 11 | | | |
---------------------------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("RR"=1)
2 - filter(RANK() OVER ( PARTITION BY
"H"."STAT_NAME","H"."INSTANCE_NAME","H"."DATABASE_ID","H"."SERVER",TRUNC(INTERNAL_FUNCTION("H"."
SNAP_TIME")) ORDER BY INTERNAL_FUNCTION("SNAP_TIME") DESC )<=1)
5 - filter("SNAP_TIME">=SYSDATE@!-3)
and it's nice as there is a PARTITION RANGE ITERATOR (so not all range
partitions are used at all) and the Filter is quite early.
But if I change the same filter down to the "outer" subquery:
with raw_data as (select /*+ NO_INDEX( h ) */ h.*, h.snap_time snap_time2
from sysstat_metrics h
where 1=1
-- and snap_time >= sysdate - 3
), better as (
select stat_name, instance_name, database_id, server, trunc(snap_time)
trunc_snap, snap_time, value, rank()
OVER (PARTITION BY STAT_NAME, instance_name,database_id, server,
trunc(SNAP_TIME) ORDER BY SNAP_TIME desc) as rr
from raw_data)
select
-- BX012
*
from better
where rr=1
and stat_name='physical read bytes'
and snap_time >= sysdate - 3
;
The plan changes to ugly
Plan hash value: 2132163184
-------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows |
A-Time | Buffers | Reads | Writes | OMem | 1Mem | Used-Mem | Used-Tmp|
-------------------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 2868
|00:00:34.24 | 100K| 38026 | 32252 | | | | |
|* 1 | VIEW | | 1 | 9387K| 2868
|00:00:34.24 | 100K| 38026 | 32252 | | | | |
|* 2 | WINDOW SORT PUSHED RANK| | 1 | 9387K|
388K|00:00:34.06 | 100K| 38026 | 32252 | 204M| 4789K| 8362K (3)|
192K|
| 3 | PARTITION LIST SINGLE | | 1 | 9387K|
9503K|00:00:03.45 | 100K| 5774 | 0 | | | |
|
| 4 | PARTITION RANGE ALL | | 1 | 9387K|
9503K|00:00:02.51 | 100K| 5774 | 0 | | | |
|
| 5 | TABLE ACCESS FULL | SYSSTAT_METRICS | 27 | 9387K|
9503K|00:00:01.49 | 100K| 5774 | 0 | | | |
|
-------------------------------------------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter(("RR"=1 AND "SNAP_TIME">=SYSDATE@!-3))
2 - filter(RANK() OVER ( PARTITION BY
"H"."STAT_NAME","H"."INSTANCE_NAME","H"."DATABASE_ID","H"."SERVER",TRUNC(INTERNAL_FUNCTION("H"."SNAP_TIME"))
ORDER BY INTERNAL_FUNCTION("H"."SNAP_TIME") DESC )<=1)
Here the statement uses much more partitions
and the filter is much later.
I am aware there is a slightly difference if I filter snap_time >= sysdate - 3
in early with clause or after the PARTITON BY window function - but such
oddities would be acceptable for this kind of data ;-).
Does anyone have an idea how I can to PARTITION RANGE ITERATOR with a filter on
the snap_time, which is the order/rank in PARTITION BY?
(before anyone asks, the NO_INDEX is to avoid this "good" plan which doesn't
change anything, but could be confusing)
| 4 | PARTITION RANGE ITERATOR | |
1 | 3 | 51612 |00:00:00.05 | 20177 | | | |
| 5 | TABLE ACCESS BY LOCAL INDEX ROWID BATCHED| SYSSTAT_METRICS |
4 | 3 | 51612 |00:00:00.04 | 20177 | | | |
|* 6 | INDEX RANGE SCAN | I_SYSSTAT_METRICS |
1 | 3 | 51612 |00:00:00.01 | 174 | | | |
--------------------------------------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter("RR"=1)
2 - filter(RANK() OVER ( PARTITION BY
"H"."STAT_NAME","H"."INSTANCE_NAME","H"."DATABASE_ID","H"."SERVER",TRUNC(INTERNAL_FUNCTION("H"."SNAP_TIME"))
ORDER BY INTERNAL_FUNCTION("SNAP_TIME") DESC )<=1)
6 - access("SNAP_TIME">=SYSDATE@!-3)
thank you for any advise,
Martin
Table definition:
CREATE TABLE "H3G_SYSSTAT_METRICS"
( "STAT_NAME" VARCHAR2(64 BYTE) NOT NULL ENABLE,
"SNAP_TIME" DATE NOT NULL ENABLE,
"DATABASE_ID" NUMBER NOT NULL ENABLE,
"INSTANCE_NAME" VARCHAR2(64 BYTE) NOT NULL ENABLE,
"SERVER" VARCHAR2(64 BYTE) NOT NULL ENABLE,
"STARTUP_TIME" DATE NOT NULL ENABLE,
"VALUE" NUMBER NOT NULL ENABLE
)
PCTFREE 0 PCTUSED 40 INITRANS 1 MAXTRANS 255
COMPRESS BASIC
STORAGE(
BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT)
TABLESPACE "USERS"
PARTITION BY LIST ("STAT_NAME")
SUBPARTITION BY RANGE ("SNAP_TIME")
(PARTITION "P2" VALUES ('CPU used by this session')
PCTFREE 0 PCTUSED 40 INITRANS 1 MAXTRANS 255
STORAGE(
BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT)
TABLESPACE "USERS"
COMPRESS BASIC
( SUBPARTITION "P2_000000" VALUES LESS THAN (TO_DATE(' 2016-01-01 00:00:00',
'SYYYY-MM-DD HH24:MI:SS', 'NLS_CALENDAR=GREGORIAN'))
TABLESPACE "USERS"
COMPRESS BASIC ,
SUBPARTITION "P2_201600" VALUES LESS THAN (TO_DATE(' 2017-01-01 00:00:00',
'SYYYY-MM-DD HH24:MI:SS', 'NLS_CALENDAR=GREGORIAN'))
TABLESPACE "USERS"
...
