Greenplum如何选择表的存储方式---heap table or append optimized table?

Greenplum在创建表的时候可以选择表存储方式，比如是行存储，还是列存储，是普通的heap表，还是append optimized表。
下面分别介绍以下
行存储是行为单位存储数据，一行中越是靠后的列，那么查询需要的cost相对越大，这个以前oracle做过相应比较，都是一样的道理，行存储更适合OLTP的系统

列存储是以列为单位存储数据，物理上一列会对应一个或者多个数据文件，而且列存储的压缩比比较高，但是如果查询的时候，如果返回的列很多，那么效率不如行存储，列存储更适合对某一列做相关统计，列存储更适合OLAP的系统

堆表，我们普通的创建的表默认都是堆表，适合频繁的更新删除操作的小表，适合OLTP系统

AO表，适合批量数据写入，不适合单行的insert,适合大表使用，所以一般用在数据仓库系统，适合OLAP系统

创建一个heap表
CREATE TABLE foo (a int, b text) DISTRIBUTED BY (a);

不带压缩的ao表
CREATE TABLE bar (a int, b text) 
    WITH (appendonly=true)
    DISTRIBUTED BY (a);


创建列存储表
CREATE TABLE bar (a int, b text) 
    WITH (appendonly=true, orientation=column)
    DISTRIBUTED BY (a);

另外压缩，可以分为列压缩，以及表压缩

列压缩和表压缩支持的算法

表存储类型	可用的压缩类型	支持的算法
Row	Table	ZLIB and QUICKLZ1
Column	Column and Table	RLE_TYPE, ZLIB, andQUICKLZ1

这里可以看到，行存储类型的只能在表级别压缩，支持ZLIB和QUICKLZ压缩算法

列存储类型可以选择表级别的压缩，也可以选择列级别的压缩，支持的压缩算法多了RLE_TYPE

创建压缩表
CREATE TABLE foo (a int, b text) 
   WITH (appendonly=true, compresstype=zlib, compresslevel=5);

检查AO表的压缩率和分布的内置函数

函数	返回类型	描述
get_ao_distribution(name) get_ao_distribution(oid)	Set of (dbid, tuplecount) rows	Shows the distribution of an append-optimized table's rows across the array. Returns a set of rows, each of which includes a segment dbid and the number of tuples stored on the segment.
get_ao_compression_ratio(name) get_ao_compression_ratio(oid)	float8	Calculates the compression ratio for a compressed append-optimized table. If information is not available, this function returns a value of -1.

列级别压缩参数介绍

• Compression type    压缩类型
• Compression level   压缩级别
• Block size for a column   列的块大小

Name	Definition	Values	Comment
COMPRESSTYPE	压缩类型	zlib: deflate algorithm quicklz: fast compression RLE_TYPE: run-length encoding none: no compression	Values are not case-sensitive.
COMPRESSLEVEL	压缩级别	zlib compression: 1-9	1最快，但是压缩比最低 9最慢，但是压缩比最高
		QuickLZcompression: 1 – use compression	默认值为1
		RLE_TYPEcompression: 1 – 4 1 - apply RLE only 2 - apply RLE then apply zlib compression level 1 3 - apply RLE then apply zlib compression level 5 4 - apply RLE then apply zlib compression level 9	1 is the fastest method with the least compression. 4 is the slowest method with the most compression. 1 is the default.
BLOCKSIZE	表中每一个块的大小	8192 – 2097152	值必须是8192的倍数，最大值为2097152，也就是2M

如果什么参数都不写，那么默认不压缩，块大小就是服务端参数设置的块大小

压缩参数设置的优先权

表级别指定的列压缩设置优先于整个表的压缩设置

分区指定的列压缩设置优先于任何表或者列的压缩设置

子分区指定的列压缩设置优先于任何表，列，以及分区的压缩设置

当一个encoding设置的参数和with设置的参数冲突，那么encoding参数的优先级高于with设置的参数

压缩参数设置的相关例子：

例1：

CREATE TABLE T1 (c1 int ENCODING (compresstype=zlib),
                  c2 char ENCODING (compresstype=quicklz, blocksize=65536),
                  c3 char )    WITH (appendonly=true, orientation=column);    --官方文档少一又括号

c1 zlib压缩类型,c2 quicklz压缩类型，块大小为65536, c3 不压缩，块大小为服务端配置文件的数据块大小，整个表为列存储的AO表

例2：

CREATE TABLE T2 (c1 int ENCODING (compresstype=zlib),
                  c2 char ENCODING (compresstype=quicklz, blocksize=65536),
                  c3 char,
                  COLUMN c3 ENCODING (compresstype=RLE_TYPE)
                  )
    WITH (appendonly=true, orientation=column)

C1压缩类型为zlib，C2压缩类型为quicklz，块大小为65536，c3压缩类型为RLE_TYPE,块大小为系统默认块大小

例3：

CREATE TABLE T3 (c1 int ENCODING (compresstype=zlib),
                  c2 char ENCODING (compresstype=quicklz, blocksize=65536),
                  c3 char, COLUMN c3 ENCODING (compresstype=RLE_TYPE) )
    WITH (appendonly=true, orientation=column)
    PARTITION BY RANGE (c3) (START ('1900-01-01'::DATE)          
                             END ('2100-12-31'::DATE),
                             COLUMN c3 ENCODING (zlib));

这里c1，zlib压缩，c2,为quicklz压缩，块大小65536，c3,注意partition为zlib,不是表级别设置的RLE_TYPE.因为partition的优先级高于table的优先级。

例4：

CREATE TABLE T4 (c1 int ENCODING (compresstype=zlib),
                  c2 char,
                  c4 smallint ENCODING (compresstype=none),
                  DEFAULT COLUMN ENCODING (compresstype=quicklz,
                                             blocksize=65536),
                  COLUMN c3 ENCODING (compresstype=RLE_TYPE)
                  ) 
   WITH (appendonly=true, orientation=column);

c1为zlib压缩，c2为quicklz压缩，块大小为65536，c3为RLE_TYPE,块大小为65536，c4无压缩类型，块大小为65536

这里注意设置的默认列的参数，如果没有在encoding命令指定参数，那么久用默认设置的参数。

例5：

CREATE TABLE T5(i int, j int, k int, l int) 
    WITH (appendonly=true, orientation=column)
    PARTITION BY range(i) SUBPARTITION BY range(j)
    (
       partition p1 start(1) end(2)
       ( subpartition sp1 start(1) end(2) 
         column i encoding(compresstype=zlib, blocksize=65536)
       ), 
       partition p2 start(2) end(3)
       ( subpartition sp1 start(1) end(2)
           column i encoding(compresstype=rle_type)
           column k encoding(blocksize=8192)
       )
    );                             --官方文档又少一个关键字partition

这里p1分区的子分区sp1中的列i压缩类型为zlib，块大小为65536，p2的sp1中的i压缩类型为rle_type,块大小为默认的块大小

自定义一个type,然后把type指定给表的列

CREATE TYPE comptype (
   internallength = 4,
   input = comptype_in,
   output = comptype_out,
   alignment = int4,
   default = 123,
   passedbyvalue,
   compresstype="quicklz",
   blocksize=65536,
   compresslevel=1
   );

CREATE TABLE t2 (c1 comptype) WITH (APPENDONLY=true, ORIENTATION=column);

alter修改表

设置非空约束

ALTER TABLE address ALTER COLUMN street SET NOT NULL;

修改表的分布策略，修改分布策略后，数据会自动重新分布

ALTER TABLE address ALTER COLUMN street SET NOT NULL;

修改表的存储模式

创建一个空表，从原表插入数据，删除原表，重命名新表，赋予所有权限

CREATE TABLE sales2 (LIKE sales) 
WITH (appendonly=true, compresstype=quicklz, 
      compresslevel=1, orientation=column);
INSERT INTO sales2 SELECT * FROM sales;
DROP TABLE sales;
ALTER TABLE sales2 RENAME TO sales;
GRANT ALL PRIVILEGES ON sales TO admin;
GRANT SELECT ON sales TO guest;

给一个表增加一个压缩列

ALTER TABLE T1
      ADD COLUMN c4 int DEFAULT 0
      ENCODING (COMPRESSTYPE=zlib);

压缩设置的继承

CREATE TABLE ccddl (i int, j int, k int, l int)
  WITH
    (APPENDONLY = TRUE, ORIENTATION=COLUMN)
  PARTITION BY range(j)
  SUBPARTITION BY list (k)
  SUBPARTITION template(
    SUBPARTITION sp1 values(1, 2, 3, 4, 5),
    COLUMN i ENCODING(COMPRESSTYPE=ZLIB),
    COLUMN j ENCODING(COMPRESSTYPE=QUICKLZ),
    COLUMN k ENCODING(COMPRESSTYPE=ZLIB),
    COLUMN l ENCODING(COMPRESSTYPE=ZLIB))
  (PARTITION p1 START(1) END(10),
   PARTITION p2 START(10) END(20))
;

ALTER TABLE ccddl
  ADD PARTITION p3 START(20) END(30)
;

gpadmin=# \dt+ ccddl*
                                    List of relations
 Schema |           Name           | Type  |  Owner  |       Storage        | Description 
--------+--------------------------+-------+---------+----------------------+-------------
 public | ccddl                    | table | gpadmin | append only columnar | 
 public | ccddl_1_prt_p1           | table | gpadmin | append only columnar | 
 public | ccddl_1_prt_p1_2_prt_sp1 | table | gpadmin | append only columnar | 
 public | ccddl_1_prt_p2           | table | gpadmin | append only columnar | 
 public | ccddl_1_prt_p2_2_prt_sp1 | table | gpadmin | append only columnar | 
 public | ccddl_1_prt_p3           | table | gpadmin | append only columnar | 
 public | ccddl_1_prt_p3_2_prt_sp1 | table | gpadmin | append only columnar | 

 gpadmin=# \d+ ccddl_1_prt_p1_2_prt_sp1
                       Append-Only Columnar Table "public.ccddl_1_prt_p1_2_prt_sp1"
 Column |  Type   | Modifiers | Storage | Compression Type | Compression Level | Block Size | Description 
--------+---------+-----------+---------+------------------+-------------------+------------+-------------
 i      | integer |           | plain   | zlib             | 1                 | 32768      | 
 j      | integer |           | plain   | quicklz          | 1                 | 32768      | 
 k      | integer |           | plain   | zlib             | 1                 | 32768      | 
 l      | integer |           | plain   | zlib             | 1                 | 32768      | 
Checksum: t
Check constraints:
    "ccddl_1_prt_p1_2_prt_sp1_check" CHECK (k = 1 OR k = 2 OR k = 3 OR k = 4 OR k = 5)
    "ccddl_1_prt_p1_check" CHECK (j >= 1 AND j < 10)
Inherits: ccddl_1_prt_p1
Has OIDs: no
Options: appendonly=true, orientation=column
Distributed by: (i)

gpadmin=# \d+ ccddl_1_prt_p3_2_prt_sp1
                       Append-Only Columnar Table "public.ccddl_1_prt_p3_2_prt_sp1"
 Column |  Type   | Modifiers | Storage | Compression Type | Compression Level | Block Size | Description 
--------+---------+-----------+---------+------------------+-------------------+------------+-------------
 i      | integer |           | plain   | zlib             | 1                 | 32768      | 
 j      | integer |           | plain   | quicklz          | 1                 | 32768      | 
 k      | integer |           | plain   | zlib             | 1                 | 32768      | 
 l      | integer |           | plain   | zlib             | 1                 | 32768      | 
Checksum: t
Check constraints:
    "ccddl_1_prt_p3_2_prt_sp1_check" CHECK (k = 1 OR k = 2 OR k = 3 OR k = 4 OR k = 5)
    "ccddl_1_prt_p3_check" CHECK (j >= 20 AND j < 30)
Inherits: ccddl_1_prt_p3
Has OIDs: no
Options: appendonly=true, orientation=column
Distributed by: (i)

通过以上的实例看到新增p3的sp1子分区ccddl_1_prt_p3_2_prt_sp1继承了子分区设置的压缩属性