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
*PG*
```
testdb=# create table t_olap(id int,c1 int,c2 varchar(20));
CREATE TABLE                           
testdb=# insert into t_olap 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_olap;
                                                                  QUERY PLAN                                                 
                 
-------------------------------------------------------------------------------------------------
 Finalize Aggregate  (cost=69209.40..69209.40 rows=1 width=72) (actual time=925.540..925.540 rows=1 loops=1)
   ->  Gather  (cost=69209.17..69209.38 rows=2 width=72) (actual time=925.284..932.688 rows=3 loops=1)
         Workers Planned: 2
         Workers Launched: 2
         ->  Partial Aggregate  (cost=68209.17..68209.18 rows=1 width=72) (actual time=911.539..911.539 rows=1 loops=3)
               ->  Parallel Seq Scan on t_olap  (cost=0.00..52584.24 rows=2083324 width=17) (actual time=0.037..240.287 rows=
1666667 loops=3)
 Planning Time: 22.703 ms
 Execution Time: 933.020 ms
(8 rows)
```
執行時間為933ms

testdb=# insert into t_olap select x,x,'c2'||x from generate_series(1,5000000) as x;
INSERT 0 5000000
```
執行查詢
```
testdb=# explain analyze select avg(id),sum(c1),max(c2) from t_olap;
                                                                  QUERY PLAN                                                 
                 
-------------------------------------------------------------------------------------------------
 Finalize Aggregate  (cost=31425.10..31425.11 rows=1 width=72) (actual time=1707.755..1707.756 rows=1 loops=1)
   ->  Gather  (cost=31424.87..31425.08 rows=2 width=72) (actual time=1659.121..1710.512 rows=3 loops=1)
         Workers Planned: 2
         Workers Launched: 2
         ->  Partial Aggregate  (cost=30424.87..30424.88 rows=1 width=72) (actual time=1647.216..1647.217 rows=1 loops=3)
               ->  Parallel Seq Scan on t_olap  (cost=0.00..24130.07 rows=839307 width=17) (actual time=0.418..1124.465 rows=
1666667 loops=3)
 Planning Time: 1.907 ms
 Execution Time: 1753.191 ms
(8 rows)
```
執行時間為1753ms,列式儲存似乎沒有發揮作用?待續.

**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(60) - 列式儲存zedstore

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