Re:Re: BUG #15173: why small gin_fuzzy_search_limit search more blocks than big gin_fuzzy_search_limit ?

1、

create table tbl_dict (
dim text, -- 维度
val int8 not null unique, -- 维度内的映射值(为了让所有维度可以打到一个数组里面，取值空间唯一)
info text -- 原始值、描述
);

create index idx_tbl_dict_1 on tbl_dict(dim,info);

select val from tbl_dict where dim=? and info=?;

2、

create table tbl_lab (
id serial8 primary key, -- 主键
dict int8[], -- N个dim，则有N个元素
score float4, -- 打分
itemid int8 -- 比如商品ID(或其他最终用户要的ID)
);

-- 不能颗粒化的维度，依旧保留放在tbl_lab表中。

select itemid from tbl_lab where dim1=? and dim10=? and dim12=? order by score desc limit 100;

set gin_fuzzy_search_limit=2000;
select * from tbl_lab where dict = any (array(
select val from tbl_dict where (dim,info) in (('1',?), ('10',?), ('12',?))
))
order by score desc limit 100;

3、

create index idx_tbl_lab_dict on tbl_lab using gin (dict);

4、

insert into tbl_dict select (random()*99)::int, generate_series(1,10000000), md5(random()::text);

create or replace function get_val(text) returns int8 as $$
select val from tbl_dict tablesample system (0.1) where dim=$1 limit 1;
$$ language sql strict;

create or replace function get_vals() returns int8[] as $$
select array_agg(get_val(id::text)) from generate_series(0,99) t(id);
$$ language sql strict;

insert into tbl_lab select get_vals(), random()*1000, random()*100000000 from generate_series(1,100);

pgbench -M prepared -n -r -P 1 -f ./test.sql -c 56 -j 56 -t 17857

public | tbl_lab | table | postgres | 81 GB |
public | idx_tbl_lab_dict | index | postgres | tbl_lab | 425 GB |

5、

create or replace function get_vals1(int) returns int8[] as $$
select array_agg(get_val(id::text)) from (select generate_series(0,99) order by random() limit $1) t(id);
$$ language sql strict stable;

set gin_fuzzy_search_limit=2000;

select * from tbl_lab where dict @> get_vals1(5)
order by score desc limit 100;

postgres=# set gin_fuzzy_search_limit =1;
SET
Time: 0.213 ms
postgres=# select count(*) from tbl_lab where dict @> array[122562]::int8[] ;
count
-------
80
(1 row)

Time: 647.802 ms
postgres=# select count(*) from tbl_lab where dict @> array[122562]::int8[] ;
count
-------
76
(1 row)

Time: 1087.094 ms (00:01.087)
postgres=# set gin_fuzzy_search_limit =10;
SET
Time: 0.174 ms
postgres=# select count(*) from tbl_lab where dict @> array[122562]::int8[] ;
count
-------
83
(1 row)

Time: 198.663 ms
postgres=# select count(*) from tbl_lab where dict @> array[122562]::int8[] ;
count
-------
3244
(1 row)

Time: 78.824 ms
postgres=# set gin_fuzzy_search_limit =100;
SET
Time: 0.202 ms
postgres=# select count(*) from tbl_lab where dict @> array[122562]::int8[] ;
count
-------
4718
(1 row)

Time: 54.961 ms
postgres=# select count(*) from tbl_lab where dict @> array[122562]::int8[] ;
count
-------
4881
(1 row)

Time: 49.879 ms
postgres=# set gin_fuzzy_search_limit =1000;
SET
Time: 0.176 ms
postgres=# select count(*) from tbl_lab where dict @> array[122562]::int8[] ;
count
-------
5783
(1 row)

Time: 46.311 ms
postgres=# select count(*) from tbl_lab where dict @> array[122562]::int8[] ;
count
-------
5784
(1 row)

Time: 45.930 ms

postgres=# set gin_fuzzy_search_limit =5000;
SET
Time: 0.219 ms
postgres=# select count(*) from tbl_lab where dict @> array[122562]::int8[] ;
count
-------
9156
(1 row)

Time: 48.888 ms
postgres=# select count(*) from tbl_lab where dict @> array[122562]::int8[] ;
count
-------
9382
(1 row)

Time: 49.479 ms
postgres=# select count(*) from tbl_lab where dict @> array[122562]::int8[] ;
count
-------
9265
(1 row)

Time: 48.514 ms
postgres=# set gin_fuzzy_search_limit =20000;
SET
Time: 0.231 ms
postgres=# select count(*) from tbl_lab where dict @> array[122562]::int8[] ;
count
-------
22432
(1 row)

Time: 58.063 ms
postgres=# select count(*) from tbl_lab where dict @> array[122562]::int8[] ;
count
-------
22746
(1 row)

Time: 56.720 ms

problem:

postgres=# set gin_fuzzy_search_limit =10;
SET
Time: 0.188 ms
postgres=# explain (analyze,verbose,timing,costs,buffers) select count(*) from tbl_lab where dict @> array[122562]::int8[] ;
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=1702903.64..1702903.65 rows=1 width=8) (actual time=135.104..135.104 rows=1 loops=1)
Output: count(*)
Buffers: shared hit=145266
-> Bitmap Heap Scan on public.tbl_lab (cost=3868.90..1701675.35 rows=491316 width=0) (actual time=135.044..135.082 rows=78 loops=1)
Recheck Cond: (tbl_lab.dict @> '{122562}'::bigint[])
Heap Blocks: exact=78
Buffers: shared hit=145266
-> Bitmap Index Scan on idx_tbl_lab_dict (cost=0.00..3746.07 rows=491316 width=0) (actual time=96.252..96.252 rows=78 loops=1)
Index Cond: (tbl_lab.dict @> '{122562}'::bigint[])
Buffers: shared hit=145248
Planning Time: 0.190 ms
JIT:
Functions: 5
Generation Time: 1.091 ms
Inlining: true
Inlining Time: 5.746 ms
Optimization: true
Optimization Time: 22.590 ms
Emission Time: 10.321 ms
Execution Time: 136.271 ms
(20 rows)

Time: 136.887 ms
postgres=# set gin_fuzzy_search_limit =5000;
SET
Time: 0.222 ms
postgres=# explain (analyze,verbose,timing,costs,buffers) select count(*) from tbl_lab where dict @> array[122562]::int8[] ;
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=1702903.64..1702903.65 rows=1 width=8) (actual time=48.953..48.953 rows=1 loops=1)
Output: count(*)
Buffers: shared hit=187
-> Bitmap Heap Scan on public.tbl_lab (cost=3868.90..1701675.35 rows=491316 width=0) (actual time=45.491..48.031 rows=9290 loops=1)
Recheck Cond: (tbl_lab.dict @> '{122562}'::bigint[])
Heap Blocks: exact=9223
Buffers: shared hit=187
-> Bitmap Index Scan on idx_tbl_lab_dict (cost=0.00..3746.07 rows=491316 width=0) (actual time=5.027..5.027 rows=9290 loops=1)
Index Cond: (tbl_lab.dict @> '{122562}'::bigint[])
Buffers: shared hit=166
Planning Time: 0.165 ms
JIT:
Functions: 5
Generation Time: 1.154 ms
Inlining: true
Inlining Time: 6.152 ms
Optimization: true
Optimization Time: 22.501 ms
Emission Time: 10.273 ms
Execution Time: 50.183 ms
(20 rows)

Time: 50.771 ms

best regards,
digoal

--
公益是一辈子的事,I'm Digoal,Just Do It.

在 2018-04-26 08:52:16，"Jeff Janes" <jeff(dot)janes(at)gmail(dot)com> 写道：

On Wed, Apr 25, 2018 at 10:53 AM, PG Bug reporting form <noreply(at)postgresql(dot)org> wrote:
The following bug has been logged on the website:

Bug reference: 15173
Logged by: Zhou Digoal
Email address: digoal(at)126(dot)com
PostgreSQL version: 10.3
Operating system: CentOS 7.x x64

I don't think you are using 10.3, because that doesn't have any JIT output in its explain plans, like you show.

I also can't reproduce the issue. What git commit are you compiling? What llvm and clang versions are you using? What non-default settings are you using? Can you reproduce the issue if you set JIT to off?

Also, can you post the data, or post a query which can be used to generate data, which produces the issue?

Cheers,

Jeff