本節簡單介紹了Greenplum開源的列式儲存zedstore的安裝和使用.

**安裝**
從Github上下載原始碼,與普通PG一樣,編譯安裝即可
```
[root@localhost postgres-zedstore]# ./configure --enable-debug --with-python --with-perl --with-tcl --with-gssapi --with-pam --with-openssl --with-pam --without-ldap --with-libxml --with-libxslt --enable-dtrace --enable-depend --enable-cassert --with-systemd CFLAGS="-O0 -DOPTIMIZER_DEBUG -g3 -gdwarf-2" --prefix=/appdb/zedstore
checking build system type... x86_64-pc-linux-gnu
...
[root@localhost postgres-zedstore]# make -j4
...
[root@localhost postgres-zedstore]# make install
...
PostgreSQL installation complete.
```

**Heap vs ZedStore**
建立使用者,初始化資料庫
```
[zedstore@localhost ~]$ initdb -E utf8 -D /data/zedstore/testdb
The files belonging to this database system will be owned by user "zedstore".
This user must also own the server process.

The database cluster will be initialized with locale "en_US.UTF-8".
The default text search configuration will be set to "english".

Data page checksums are disabled.

creating directory /data/zedstore/testdb ... ok
creating subdirectories ... ok
selecting dynamic shared memory implementation ... posix
selecting default max_connections ... 100
selecting default shared_buffers ... 128MB
selecting default timezone ... PRC
creating configuration files ... ok
running bootstrap script ... ok
performing post-bootstrap initialization ... ok
syncing data to disk ... ok

initdb: warning: enabling "trust" authentication for local connections
You can change this by editing pg_hba.conf or using the option -A, or
--auth-local and --auth-host, the next time you run initdb.

Success. You can now start the database server using:

pg_ctl -D /data/zedstore/testdb -l logfile start

```
下面來對比一下head am和zedstore的效能差異
*Heap*
```
testdb=# create table t_heap(id int,c1 int,c2 varchar(20));
CREATE TABLE                           
testdb=# insert into t_heap select x,x,'c2'||x from generate_series(1,5000000) as x;
INSERT 0 5000000
testdb=# 
```
執行查詢
```
testdb=# explain analyze select avg(id),sum(c1),max(c2) from t_heap;
                                                                  QUERY PLAN                                      
                            
------------------------------------------------------------------------------------------------------------------
----------------------------
 Finalize Aggregate  (cost=69209.94..69209.95 rows=1 width=72) (actual time=964.313..964.314 rows=1 loops=1)
   ->  Gather  (cost=69209.71..69209.92 rows=2 width=72) (actual time=963.978..966.938 rows=3 loops=1)
         Workers Planned: 2
         Workers Launched: 2
         ->  Partial Aggregate  (cost=68209.71..68209.72 rows=1 width=72) (actual time=929.220..929.220 rows=1 loo
ps=3)
               ->  Parallel Seq Scan on t_heap  (cost=0.00..52584.55 rows=2083355 width=17) (actual time=0.094..25
6.014 rows=1666667 loops=3)
 Planning Time: 17.157 ms
 Execution Time: 968.461 ms
(8 rows)

testdb=#

```
執行時間為968ms

空間佔用
```
testdb=# select pg_size_pretty(pg_table_size('t_heap'));
 pg_size_pretty 
----------------
 248 MB
(1 row)

```

*ZedStore*
```
testdb=# create table t_zedstore(id int,c1 int,c2 varchar(20)) using zedstore;
CREATE TABLE                           
testdb=# insert into t_zedstore select x,x,'c2'||x from generate_series(1,5000000) as x;
INSERT 0 5000000
testdb=# 
```
執行查詢
```
testdb=# explain analyze select avg(id),sum(c1),max(c2) from t_zedstore;
                                                                   QUERY PLAN                                     
                               
------------------------------------------------------------------------------------------------------------------
-------------------------------
 Finalize Aggregate  (cost=24917.50..24917.51 rows=1 width=72) (actual time=1341.238..1341.239 rows=1 loops=1)
   ->  Gather  (cost=24917.27..24917.48 rows=2 width=72) (actual time=1341.046..1343.387 rows=3 loops=1)
         Workers Planned: 2
         Workers Launched: 2
         ->  Partial Aggregate  (cost=23917.27..23917.28 rows=1 width=72) (actual time=1328.432..1328.432 rows=1 l
oops=3)
               ->  Parallel Seq Scan on t_zedstore  (cost=0.00..18968.87 rows=659787 width=17) (actual time=0.702.
.837.075 rows=1666667 loops=3)
 Planning Time: 0.643 ms
 Execution Time: 1343.612 ms
(8 rows)

testdb=#

```
使用zedstore的時間是1343ms，比起heap方式要慢接近40%。

空間佔用
```
testdb=# select pg_size_pretty(pg_table_size('t_zedstore'));
 pg_size_pretty 
----------------
 97 MB
(1 row)

testdb=# 
```
不過使用zedstore，空間佔用倒是隻有原來的40%左右。

**參考資料**
[PostgreSQL 基於access method api的列存zedstore](https://github.com/digoal/blog/blob/master/201905/20190531_03.md)

PostgreSQL DBA(123) - 列式儲存zedstore再體驗

相關文章