Bloom Filter For Non-Parallel query on Non-Partition Table

I notice an enhancement in 12.1.0.2.0 beta, bloom filter is enabled for non-parallel query on non-partition table. The enhancement may help improve the hash join performance, this page show a little demo. The testing is on Exadata X4-2 instance.

> SELECT * FROM PRODUCT_COMPONENT_VERSION;

PRODUCT          VERSION        STATUS
---------------------------------------- -------------------- --------------------
NLSRTL           12.1.0.2.0       Beta
Oracle Database 12c Enterprise Edition   12.1.0.2.0       64bit Beta
PL/SQL           12.1.0.2.0       Beta
TNS for Linux:         12.1.0.2.0       Beta

> select platform_id, platform_name from v$database;

PLATFORM_ID PLATFORM_NAME
----------- ----------------
   13 Linux x86 64-bit

Prepare two table for hash join, 10k rows in t1 and 10m rows in t2. 100 records for each value on the column t1.n1 and t2.n1.

drop table t1;
drop table t2;

-- t1 with 10,000 rows
create table t1
as
select
    rownum                      id,
    lpad(rownum, 10, '0')       v1,
    trunc((rownum - 1)/100)     n1,
    rpad(rownum, 100)           padding
from
    dual
connect by level <= 10000
;

-- t2 with 10,000,000 rows
create table t2
as
select
    rownum                      id,
    lpad(rownum, 10, '0')       v1,
    trunc((rownum - 1)/100)     n1,
    rpad(rownum, 100)           padding
from
    t1, t1
where
    rownum <= 1e7;

begin
    dbms_stats.gather_table_stats(
        ownname      => user,
        tabname      =>'T1',
        method_opt   => 'for all columns size 1'
    );

    dbms_stats.gather_table_stats(
        ownname      => user,
        tabname      =>'T2',
        method_opt   => 'for all columns size 1'
    );
end;
/

The hash join between t1 and t2 return only 100 rows, if the bloom filter is created after t1 is scanned, and applied on t2 when t2 is scanned, most of the rows of t2 is filtered at the first place. The sql monitor report show that how bloom filter takes effect. With bloom filter enabled, the rows returned from smart scan on t2 is 15k, cell offload efficiency is 100%(only 2MB bytes returned from Exadata). Without bloom filter, the rows returned from smart scan on t2 is 10M, cell offload efficiency is 84%(230MB bytes returned from Exadata).

alter system flush buffer_cache;
select
    /*+ monitor */
    count(t2.v1)
from
    t1, t2
where
    t1.id = t2.id
and t1.n1 = 0;

alter system flush buffer_cache;
select
    /*+ monitor no_px_join_filter(t2) */
    count(t2.v1)
from
    t1, t2
where
    t1.id = t2.id
and t1.n1 = 0;

Update on Mar 25th

Serial generation for bloom filters on Exadata is enabled in 12.1.0.2, and backported to 11.2.0.4 with bug 16710321. Hidden parameter _bloom_serial_filter control the function.

> @pd _bloom_serial_filter

NAME                  VALUE     DESCRIPTION
--------------------- --------- -------------------------------------------------------
_bloom_serial_filter  ON        enable serial bloom filter on exadata

发表评论

电子邮件地址不会被公开。 必填项已用*标注

您可以使用这些HTML标签和属性: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>