GBase 8s 普通表转换成分片表的方式分析
GBase 8s中的普通表可以通过两种方式转换成分片表：通过init初始化为分片表；通过attach加入新建的分片表。
以下面的测试表t1为例：
create table t1(col1 int, col2 datetime year to second, col3 varchar(128)) in datadbs01;
create index ix_t1_col1 on t1(col1);
以下将以col2字段按月进行表分片。
1，通过alter fragment on table TABNAME init fragment ... 方式
初始化前表t1的输出oncheck -pt testdb:t1
### 这里仅输出关心的信息
TBLspace Report for testdb:gbasedbt.t1
Physical Address 6:571
Creation date 08/05/2020 13:35:00
Index ix_t1_col1 fragment partition datadbs01 in DBspace datadbs01
Physical Address 6:573
Creation date 08/05/2020 13:35:01
执行初始化语句，具体的语句为
alter fragment on table t1 init fragment by expression
partition p0 col2 < datetime(2020-09-01 00:00:00) year to second in datadbs01,
partition p1 col2 < datetime(2020-10-01 00:00:00) year to second and col2 >= datetime(2020-09-01 00:00:00) year to second in datadbs02,
partition p2 col2 < datetime(2020-11-01 00:00:00) year to second and col2 >= datetime(2020-10-01 00:00:00) year to second in datadbs03,
partition pr remainder in datadbs04;
再次输出oncheck -pt testdb:t1
### 这里仅输出关心的信息
TBLspace Report for testdb:gbasedbt.t1
Table fragment partition p0 in DBspace datadbs01
Physical Address 6:574
Creation date 08/05/2020 13:35:41
Table fragment partition p1 in DBspace datadbs02
Physical Address 7:7
Creation date 08/05/2020 13:35:41
Table fragment partition p2 in DBspace datadbs03
Physical Address 8:7
Creation date 08/05/2020 13:35:41
Table fragment partition pr in DBspace datadbs04
Physical Address 9:7
Creation date 08/05/2020 13:35:41
Index ix_t1_col1 fragment partition datadbs01 in DBspace datadbs01
Physical Address 6:575
Creation date 08/05/2020 13:35:41
结果中显示：原有分区6:571已经变更为6:574，建表的时间也已经改变，表明有数据迁移的情况出现。
2，通过alter fragment on table FRAGMENT_TABNAME attach TABNAME ... 方式
attach操作前表t1的输出oncheck -pt testdb:t1
TBLspace Report for testdb:gbasedbt.t1
Physical Address 6:571
Creation date 08/05/2020 13:36:00
Index ix_t1_col1 fragment partition datadbs01 in DBspace datadbs01
Physical Address 6:573
Creation date 08/05/2020 13:36:01
执行attach语句，具体的语句为
-- 创建tf分片表，不包含表t1使用的分区
create table tf(col1 int, col2 datetime year to second, col3 varchar(128))
fragment by expression
partition p1 col2 < datetime(2020-10-01 00:00:00) year to second and col2 >= datetime(2020-09-01 00:00:00) year to second in datadbs02,
partition p2 col2 < datetime(2020-11-01 00:00:00) year to second and col2 >= datetime(2020-10-01 00:00:00) year to second in datadbs03,
partition pr remainder in datadbs04;
-- 创建索引，不指定in dbspace
create index ix_tf_col1 on tf(col1);
-- attach语句
ALTER FRAGMENT ON TABLE tf ATTACH t1 AS partition p0 (col2 < datetime(2020-09-01 00:00:00) year to second) before p1;
输出oncheck -pt testdb:tf
TBLspace Report for testdb:gbasedbt.tf
Table fragment partition p0 in DBspace datadbs01
Physical Address 6:571
Creation date 08/05/2020 13:36:00
Table fragment partition p1 in DBspace datadbs02
Physical Address 7:5
Creation date 08/05/2020 13:37:23
Table fragment partition p2 in DBspace datadbs03
Physical Address 8:5
Creation date 08/05/2020 13:37:23
Table fragment partition pr in DBspace datadbs04
Physical Address 9:5
Creation date 08/05/2020 13:37:23
Index ix_tf_col1 fragment partition p0 in DBspace datadbs01
Physical Address 6:573
Creation date 08/05/2020 13:36:01
Index ix_tf_col1 fragment partition p1 in DBspace datadbs02
Physical Address 7:6
Creation date 08/05/2020 13:37:58
Index ix_tf_col1 fragment partition p2 in DBspace datadbs03
Physical Address 8:6
Creation date 08/05/2020 13:37:58
Index ix_tf_col1 fragment partition pr in DBspace datadbs04
Physical Address 9:6
Creation date 08/05/2020 13:37:58
结果中显示：原有表t1的分区6:571已经变成为分片表tf的p0分区，该分区的建表时间并未改变。
综上结论：将普通表转换成分片表，最好使用attach方式，以减少数据迁移的影响。
来自 “ ITPUB博客 ” ，链接：https://blog.itpub.net/69980390/viewspace-2736725/ ，如需转载，请注明出处，否则将追究法律责任。
