PostgreSQL 14 Bottom-up index tuple deletion 大大减少btree索引膨胀
准备PG12和PG14两个环境，主要参数保持一致，并执行如下SQL初始化测试表：
CREATE TABLE testtab (
id bigint
CONSTRAINT testtab_pkey PRIMARY KEY,
unchanged integer,
changed integer
);
INSERT INTO testtab
SELECT i, i, 0
FROM generate_series(1, 10000) AS i;
CREATE INDEX testtab_unchanged_idx ON testtab (unchanged);
CREATE INDEX testtab_changed_idx ON testtab (changed);
vacuum ANALYZE testtab;PG12查看表索引大小：
postgres=# \dt+ testtab
List of relations
Schema | Name | Type | Owner | Size | Description
--------+---------+-------+----------+--------+-------------
public | testtab | table | postgres | 576 kB |
(1 row)
postgres=# \di+ testtab*
List of relations
Schema | Name | Type | Owner | Table | Size | Description
--------+-----------------------+-------+----------+---------+--------+-------------
public | testtab_changed_idx | index | postgres | testtab | 288 kB |
public | testtab_pkey | index | postgres | testtab | 288 kB |
public | testtab_unchanged_idx | index | postgres | testtab | 288 kB |
(3 rows)PG14查看表索引大小：
postgres=# \di+ testtab*
List of relations
Schema | Name | Type | Owner | Table | Persistence | Access method | Size | Description
--------+-----------------------+-------+----------+---------+-------------+---------------+--------+-------------
public | testtab_changed_idx | index | postgres | testtab | permanent | btree | 128 kB |
public | testtab_pkey | index | postgres | testtab | permanent | btree | 288 kB |
public | testtab_unchanged_idx | index | postgres | testtab | permanent | btree | 288 kB |
(3 rows)新建pgbench.sql文件并写入如下SQL:
\set id random_gaussian(1, 10000, 10)
UPDATE testtab SET changed = changed + 1 WHERE id = :id;
UPDATE testtab SET changed = changed + 1 WHERE id = :id;
UPDATE testtab SET changed = changed + 1 WHERE id = :id;
UPDATE testtab SET changed = changed + 1 WHERE id = :id;
UPDATE testtab SET changed = changed + 1 WHERE id = :id;
UPDATE testtab SET changed = changed + 1 WHERE id = :id;
UPDATE testtab SET changed = changed + 1 WHERE id = :id;
UPDATE testtab SET changed = changed + 1 WHERE id = :id;
UPDATE testtab SET changed = changed + 1 WHERE id = :id;
UPDATE testtab SET changed = changed + 1 WHERE id = :id;分别在PG12和PG14运行如下pgbench基准测试：
time pgbench -M prepared -n -c 6 -f pgbench.sql -t 10000 postgres查看索引及表大小：
PG12
postgres=# \di+ testtab*
List of relations
Schema | Name | Type | Owner | Table | Size | Description
--------+-----------------------+-------+----------+---------+---------+-------------
public | testtab_changed_idx | index | postgres | testtab | 14 MB |
public | testtab_pkey | index | postgres | testtab | 1472 kB |
public | testtab_unchanged_idx | index | postgres | testtab | 14 MB |
(3 rows)PG14
postgres=# \di+ testtab*
List of relations
Schema | Name | Type | Owner | Table | Persistence | Access method | Size | Description
--------+-----------------------+-------+----------+---------+-------------+---------------+---------+-------------
public | testtab_changed_idx | index | postgres | testtab | permanent | btree | 5248 kB |
public | testtab_pkey | index | postgres | testtab | permanent | btree | 288 kB |
public | testtab_unchanged_idx | index | postgres | testtab | permanent | btree | 512 kB |
(3 rows)可以看到明显PG14中的索引比PG12大小小的多得多。 升级！升级！升级！
原创文章，作者：奋斗，如若转载，请注明出处：https://blog.ytso.com/237367.html