PostgreSQL中不同数据类型对查询性能的影响有哪些

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容量
数据列占用空间大小

[local]:5432 pg12@testdb=# SELECT pg_column_size(SMALLINT '1'),pg_column_size(INT4 '1'), pg_column_size(NUMERIC(6,0) '1'),pg_column_size(FLOAT '1'); pg_column_size | pg_column_size | pg_column_size | pg_column_size ----------------+----------------+----------------+----------------              2 |              4 |              8 |              8

创建数据表，0和1的数据值各插入100w行，查看数据表的占用空间大小。
numeric

[local]:5432 pg12@testdb=# create table t_numeric(id numeric);CREATE TABLE[local]:5432 pg12@testdb=# [local]:5432 pg12@testdb=# insert into t_numeric select 0 from generate_series(1,1000000);INSERT 0 1000000[local]:5432 pg12@testdb=# insert into t_numeric select 1 from generate_series(1,1000000);INSERT 0 1000000[local]:5432 pg12@testdb=# select pg_size_pretty(pg_relation_size('t_numeric')); pg_size_pretty ---------------- 69 MB(1 row)

float

[local]:5432 pg12@testdb=# create table t_float(id int);CREATE TABLE[local]:5432 pg12@testdb=# [local]:5432 pg12@testdb=# insert into t_float select 0 from generate_series(1,1000000);INSERT 0 1000000[local]:5432 pg12@testdb=# insert into t_float select 1 from generate_series(1,1000000);INSERT 0 1000000[local]:5432 pg12@testdb=# [local]:5432 pg12@testdb=# select pg_size_pretty(pg_relation_size('t_float')); pg_size_pretty ---------------- 69 MB(1 row)[local]:5432 pg12@testdb=#

int

[local]:5432 pg12@testdb=# create table t_int(id int);CREATE TABLE[local]:5432 pg12@testdb=# [local]:5432 pg12@testdb=# insert into t_int select 0 from generate_series(1,1000000);INSERT 0 1000000[local]:5432 pg12@testdb=# insert into t_int select 1 from generate_series(1,1000000);INSERT 0 1000000[local]:5432 pg12@testdb=# select pg_size_pretty(pg_relation_size('t_int')); pg_size_pretty ---------------- 69 MB(1 row)

smallint

[local]:5432 pg12@testdb=# create table t_smallint(id smallint);CREATE TABLE[local]:5432 pg12@testdb=# [local]:5432 pg12@testdb=# insert into t_smallint select 0 from generate_series(1,1000000);INSERT 0 1000000[local]:5432 pg12@testdb=# insert into t_smallint select 1 from generate_series(1,1000000);INSERT 0 1000000[local]:5432 pg12@testdb=# [local]:5432 pg12@testdb=# select pg_size_pretty(pg_relation_size('t_smallint')); pg_size_pretty ---------------- 69 MB(1 row)

boolean

[local]:5432 pg12@testdb=# create table t_bool(id boolean);CREATE TABLE[local]:5432 pg12@testdb=# insert into t_bool select 0::boolean from generate_series(1,1000000);INSERT 0 1000000[local]:5432 pg12@testdb=# insert into t_bool select 1::boolean from generate_series(1,1000000);INSERT 0 1000000[local]:5432 pg12@testdb=# [local]:5432 pg12@testdb=# select pg_size_pretty(pg_relation_size('t_bool')); pg_size_pretty ---------------- 69 MB(1 row)

可以看到，四种数据类型占用的空间都是69 MB。

查询性能
不加条件，全表扫描

-- 禁用并行[local]:5432 pg12@testdb=# SET max_parallel_workers_per_gather = 0;SET[local]:5432 pg12@testdb=# explain (analyze,verbose,buffers) select count(*) from t_numeric;                                                            QUERY PLAN                                                            ---------------------------------------------------------------------------------------------------------------------------------- Aggregate  (cost=33850.00..33850.01 rows=1 width=8) (actual time=478.196..478.196 rows=1 loops=1)   Output: count(*)   Buffers: shared hit=8850   ->  Seq Scan on public.t_numeric  (cost=0.00..28850.00 rows=2000000 width=0) (actual time=0.053..255.949 rows=2000000 loops=1)         Output: id         Buffers: shared hit=8850 Planning Time: 0.716 ms Execution Time: 478.280 ms(8 rows)[local]:5432 pg12@testdb=# explain (analyze,verbose,buffers) select count(*) from t_float;                                                           QUERY PLAN                                                           -------------------------------------------------------------------------------------------------------------------------------- Aggregate  (cost=33850.00..33850.01 rows=1 width=8) (actual time=421.919..421.919 rows=1 loops=1)   Output: count(*)   Buffers: shared hit=8850   ->  Seq Scan on public.t_float  (cost=0.00..28850.00 rows=2000000 width=0) (actual time=0.010..222.624 rows=2000000 loops=1)         Output: id         Buffers: shared hit=8850 Planning Time: 0.231 ms Execution Time: 421.948 ms(8 rows)[local]:5432 pg12@testdb=# explain (analyze,verbose,buffers) select count(*) from t_int;                                                          QUERY PLAN                                                          ------------------------------------------------------------------------------------------------------------------------------ Aggregate  (cost=33850.00..33850.01 rows=1 width=8) (actual time=440.328..440.328 rows=1 loops=1)   Output: count(*)   Buffers: shared hit=8850   ->  Seq Scan on public.t_int  (cost=0.00..28850.00 rows=2000000 width=0) (actual time=0.011..236.078 rows=2000000 loops=1)         Output: id         Buffers: shared hit=8850 Planning Time: 0.208 ms Execution Time: 440.359 ms(8 rows)[local]:5432 pg12@testdb=#  explain (analyze,verbose,buffers) select count(*) from t_smallint;                                                            QUERY PLAN                                                             ----------------------------------------------------------------------------------------------------------------------------------- Aggregate  (cost=33850.00..33850.01 rows=1 width=8) (actual time=439.007..439.007 rows=1 loops=1)   Output: count(*)   Buffers: shared hit=8850   ->  Seq Scan on public.t_smallint  (cost=0.00..28850.00 rows=2000000 width=0) (actual time=0.043..232.069 rows=2000000 loops=1)         Output: id         Buffers: shared hit=8850 Planning Time: 0.553 ms Execution Time: 439.081 ms(8 rows)[local]:5432 pg12@testdb=# explain (analyze,verbose,buffers) select count(*) from t_bool;                                                          QUERY PLAN                                                           ------------------------------------------------------------------------------------------------------------------------------- Aggregate  (cost=33850.00..33850.01 rows=1 width=8) (actual time=430.800..430.800 rows=1 loops=1)   Output: count(*)   Buffers: shared hit=8850   ->  Seq Scan on public.t_bool  (cost=0.00..28850.00 rows=2000000 width=0) (actual time=0.010..230.333 rows=2000000 loops=1)         Output: id         Buffers: shared hit=8850 Planning Time: 0.224 ms Execution Time: 430.831 ms(8 rows)[local]:5432 pg12@testdb=#

不带条件全表扫描，时间相差不大，执行时长最大的是numeric类型。

添加查询条件，全表扫描

[local]:5432 pg12@testdb=# explain (analyze,verbose,buffers) select count(*) from t_numeric where id = '0'::numeric;lain (analyze,verbose,buffers) select count(*) from t_bool where id = 0::boolean;                                                            QUERY PLAN                                                            ---------------------------------------------------------------------------------------------------------------------------------- Aggregate  (cost=36358.67..36358.68 rows=1 width=8) (actual time=723.356..723.357 rows=1 loops=1)   Output: count(*)   Buffers: shared hit=8850   ->  Seq Scan on public.t_numeric  (cost=0.00..33850.00 rows=1003467 width=0) (actual time=0.057..610.907 rows=1000000 loops=1)         Output: id         Filter: (t_numeric.id = '0'::numeric)         Rows Removed by Filter: 1000000         Buffers: shared hit=8850 Planning Time: 1.901 ms Execution Time: 723.449 ms(10 rows)[local]:5432 pg12@testdb=# explain (analyze,verbose,buffers) select count(*) from t_float where id = '0'::numeric;                                                          QUERY PLAN                                                          ------------------------------------------------------------------------------------------------------------------------------ Aggregate  (cost=38875.00..38875.01 rows=1 width=8) (actual time=827.686..827.687 rows=1 loops=1)   Output: count(*)   Buffers: shared hit=8850   ->  Seq Scan on public.t_float  (cost=0.00..38850.00 rows=10000 width=0) (actual time=0.015..725.737 rows=1000000 loops=1)         Output: id         Filter: ((t_float.id)::numeric = '0'::numeric)         Rows Removed by Filter: 1000000         Buffers: shared hit=8850 Planning Time: 0.234 ms Execution Time: 827.720 ms(10 rows)[local]:5432 pg12@testdb=# explain (analyze,verbose,buffers) select count(*) from t_int where id = 0;                                                         QUERY PLAN                                                          ----------------------------------------------------------------------------------------------------------------------------- Aggregate  (cost=36329.50..36329.51 rows=1 width=8) (actual time=434.067..434.067 rows=1 loops=1)   Output: count(*)   Buffers: shared hit=8850   ->  Seq Scan on public.t_int  (cost=0.00..33850.00 rows=991800 width=0) (actual time=0.014..333.883 rows=1000000 loops=1)         Output: id         Filter: (t_int.id = 0)         Rows Removed by Filter: 1000000         Buffers: shared hit=8850 Planning Time: 0.295 ms Execution Time: 434.101 ms(10 rows)[local]:5432 pg12@testdb=# explain (analyze,verbose,buffers) select count(*) from t_smallint where id = 0;                                                            QUERY PLAN                                                             ----------------------------------------------------------------------------------------------------------------------------------- Aggregate  (cost=36354.50..36354.51 rows=1 width=8) (actual time=486.466..486.466 rows=1 loops=1)   Output: count(*)   Buffers: shared hit=8850   ->  Seq Scan on public.t_smallint  (cost=0.00..33850.00 rows=1001800 width=0) (actual time=0.053..368.184 rows=1000000 loops=1)         Output: id         Filter: (t_smallint.id = 0)         Rows Removed by Filter: 1000000         Buffers: shared hit=8850 Planning Time: 1.396 ms Execution Time: 486.554 ms(10 rows)[local]:5432 pg12@testdb=# explain (analyze,verbose,buffers) select count(*) from t_bool where id = 0::boolean;                                                          QUERY PLAN                                                           ------------------------------------------------------------------------------------------------------------------------------- Aggregate  (cost=31356.67..31356.68 rows=1 width=8) (actual time=416.510..416.510 rows=1 loops=1)   Output: count(*)   Buffers: shared hit=8850   ->  Seq Scan on public.t_bool  (cost=0.00..28850.00 rows=1002667 width=0) (actual time=0.014..316.188 rows=1000000 loops=1)         Output: id         Filter: (NOT t_bool.id)         Rows Removed by Filter: 1000000         Buffers: shared hit=8850 Planning Time: 0.261 ms Execution Time: 416.551 ms(10 rows)[local]:5432 pg12@testdb=#

存在查询条件的情况下，由于解析表达式的代价不同（bool < int < numeric < float），因此时间相差较大，时长最大的是float类型，时间接近bool类型的2倍。

创建索引，全索引扫描
禁用全表扫描，使用全索引扫描

[local]:5432 pg12@testdb=# explain (analyze,verbose,buffers) select count(*) from t_numeric where id = '0'::numeric;                                                                           QUERY PLAN                                                                           ---------------------------------------------------------------------------------------------------------------------------------------------------------------- Aggregate  (cost=35541.77..35541.78 rows=1 width=8) (actual time=594.984..594.984 rows=1 loops=1)   Output: count(*)   Buffers: shared hit=7160   ->  Index Only Scan using idx_t_numeric_id on public.t_numeric  (cost=0.43..33033.10 rows=1003467 width=0) (actual time=0.269..482.525 rows=1000000 loops=1)         Output: id         Index Cond: (t_numeric.id = '0'::numeric)         Heap Fetches: 1000000         Buffers: shared hit=7160 Planning Time: 1.392 ms Execution Time: 595.253 ms(10 rows)[local]:5432 pg12@testdb=# explain (analyze,verbose,buffers) select count(*) from t_float where id = '0'::numeric;                                                                        QUERY PLAN                                                                         ----------------------------------------------------------------------------------------------------------------------------------------------------------- Aggregate  (cost=70854.43..70854.44 rows=1 width=8) (actual time=1337.093..1337.094 rows=1 loops=1)   Output: count(*)   Buffers: shared hit=14317   ->  Index Only Scan using idx_t_float_id on public.t_float  (cost=0.43..70829.43 rows=10000 width=0) (actual time=0.037..1233.730 rows=1000000 loops=1)         Output: id         Filter: ((t_float.id)::numeric = '0'::numeric)         Rows Removed by Filter: 1000000         Heap Fetches: 2000000         Buffers: shared hit=14317 Planning Time: 0.293 ms Execution Time: 1337.168 ms(11 rows)[local]:5432 pg12@testdb=# explain (analyze,verbose,buffers) select count(*) from t_int where id = 0;                                                                      QUERY PLAN                                                                       ------------------------------------------------------------------------------------------------------------------------------------------------------- Aggregate  (cost=35128.43..35128.44 rows=1 width=8) (actual time=526.942..526.943 rows=1 loops=1)   Output: count(*)   Buffers: shared hit=7160   ->  Index Only Scan using idx_t_int_id on public.t_int  (cost=0.43..32648.93 rows=991800 width=0) (actual time=0.035..414.797 rows=1000000 loops=1)         Output: id         Index Cond: (t_int.id = 0)         Heap Fetches: 1000000         Buffers: shared hit=7160 Planning Time: 0.245 ms Execution Time: 526.979 ms(10 rows)[local]:5432 pg12@testdb=# explain (analyze,verbose,buffers) select count(*) from t_smallint where id = 0;                                                                            QUERY PLAN                                                                            ------------------------------------------------------------------------------------------------------------------------------------------------------------------ Aggregate  (cost=35480.43..35480.44 rows=1 width=8) (actual time=551.394..551.394 rows=1 loops=1)   Output: count(*)   Buffers: shared hit=4428 read=2735   ->  Index Only Scan using idx_t_smallint_id on public.t_smallint  (cost=0.43..32975.93 rows=1001800 width=0) (actual time=0.459..438.992 rows=1000000 loops=1)         Output: id         Index Cond: (t_smallint.id = 0)         Heap Fetches: 1000000         Buffers: shared hit=4428 read=2735 Planning Time: 1.889 ms Execution Time: 551.499 ms(10 rows)[local]:5432 pg12@testdb=# explain (analyze,verbose,buffers) select count(*) from t_bool where id = 0::boolean;                                                                        QUERY PLAN                                                                        ---------------------------------------------------------------------------------------------------------------------------------------------------------- Aggregate  (cost=35513.77..35513.78 rows=1 width=8) (actual time=497.886..497.886 rows=1 loops=1)   Output: count(*)   Buffers: shared hit=7160   ->  Index Only Scan using idx_t_bool_id on public.t_bool  (cost=0.43..33007.10 rows=1002667 width=0) (actual time=0.035..393.653 rows=1000000 loops=1)         Output: id         Index Cond: (t_bool.id = false)         Heap Fetches: 1000000         Buffers: shared hit=7160 Planning Time: 0.250 ms Execution Time: 497.922 ms(10 rows)[local]:5432 pg12@testdb=#

走全索引扫描，执行时长最长的仍是float类型，其他三种类型则相差不大，numeric的性能相较全表扫描有明显提升（595ms vs 723ms）。

压力测试
使用pgbench进行压力测试，numeric/float/int三种类型，各插入100w数据

drop table t_big_numeric;create table t_big_numeric(id numeric);insert into t_big_numeric select 0 from generate_series(1,1000000);drop table t_big_float;create table t_big_float(id int);insert into t_big_float select 0 from generate_series(1,1000000);drop table t_big_int;create table t_big_int(id int);insert into t_big_int select 0 from generate_series(1,1000000);

测试结果

[pg12@localhost test]$ pgbench -C -f ./select_numeric.sql --time=120 --client=8 --jobs=2 -d testdb...transaction type: ./select_numeric.sqlscaling factor: 1query mode: simplenumber of clients: 8number of threads: 2duration: 120 snumber of transactions actually processed: 1254latency average = 768.659 mstps = 10.407739 (including connections establishing)tps = 10.906626 (excluding connections establishing)[pg12@localhost test]$ [pg12@localhost test]$ pgbench -C -f ./select_float.sql --time=120 --client=8 --jobs=2 -d testdb...transaction type: ./select_float.sqlscaling factor: 1query mode: simplenumber of clients: 8number of threads: 2duration: 120 snumber of transactions actually processed: 2167latency average = 444.006 mstps = 18.017778 (including connections establishing)tps = 19.461350 (excluding connections establishing)[pg12@localhost test]$ cat select_float.sql \set id random(1,1000000)select * from t_big_float where id = :id; [pg12@localhost test]$ [pg12@localhost test]$ pgbench -C -f ./select_int.sql --time=120 --client=8 --jobs=2 -d testdb...transaction type: ./select_int.sqlscaling factor: 1query mode: simplenumber of clients: 8number of threads: 2duration: 120 snumber of transactions actually processed: 2184latency average = 440.271 mstps = 18.170626 (including connections establishing)tps = 19.658996 (excluding connections establishing)[pg12@localhost test]$

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