EsgynDB在金融行业的分支版本钱库（QianBase）已经问世有段时间，在钱库版本中，对相关的功能、性能部分做了大量的增强。这其中包括插入、更新及删除的性能提升。
在早期的版本中，当目标表只有主键的情况下，EsgynDB的增删改的性能是相当不错的，因为默认情况下执行计划走的是批量提交的方式，在执行计划中我们可以看到诸如VSBB_UPSERT、VSBB_DELETE这样的字眼，VSBB即批量执行。但当表上有一个或多个索引的时候，相比较于没有索引的情况下，性能会下降很大。
针对此问题，钱库中做了相关的性能增强，包括插入、更新及删除，都做了相应的增强。关于插入和更新，我们会在后续文章中慢慢介绍，本文中我们先对比一下DELETE的性能提升。
在早期版本中，在有索引的表上做DELETE操作时，对于表记录的删除，执行计划并没有采用VSBB_DELETE，而是走TRAFODION_DELETE，这严重限制了删除的性能，以下是一个DELETE有索引表的执行计划，
LC RC OP OPERATOR OPT DESCRIPTION CARD
---- ---- ---- -------------------- -------- -------------------- ---------
5 . 6 root x 1.19E+006
3 4 5 nested_join 1.19E+006
. . 4 trafodion_vsbb_delet IDX_TEST_DELETE 1.00E+000
1 2 3 nested_join 1.19E+006
. . 2 trafodion_delete TEST_DELETE 1.00E+000
. . 1 trafodion_scan TEST_DELETE 1.19E+006
虽然对于索引的执行计划是TRAFODION_VSBB_DELET，但由于对于主表的删除是TRAFODION_DELETE，导致语句执行效率相当低下，从以下运行时的统计信息可以看出，EX_TRAF_DELETE的OperCPUTime是71,645,451。此表总记录数100万，删除记录为99万多，删除时长超过2小时未结束。
>>get statistics for qid current default;
Qid MXID11000016667212447900982995646000000000206U3333302T000_335___SQLCI_DML_LAST__
Compile Start Time 2020/02/08 14:11:01.268632
Compile End Time 2020/02/08 14:11:01.279867
Compile Elapsed Time 0:00:00.011235
Execute Start Time 2020/02/08 14:11:01.280240
Execute End Time 2020/02/08 16:11:01.894070
Execute Elapsed Time 2:00:00.613830
State DEALLOCATED
Rows Affected 184,938
SQL Error Code -8448
Stats Error Code 0
Query Type SQL_DELETE_NON_UNIQUE
Sub Query Type SQL_STMT_NA
Estimated Accessed Rows 0
Estimated Used Rows 0
Parent Qid NONE
Parent Query System NONE
Child Qid NONE
Number of SQL Processes 1
Number of Cpus 1
Transaction Id 72339069014678765
Source String delete from test_delete where a>100;
SQL Source Length 36
Rows Returned 0
First Row Returned Time -1
Last Error before AQR 0
Number of AQR retries 0
Delay before AQR 0
No. of times reclaimed 0
Cancel Time -1
Last Suspend Time -1
Query hash 0
SLA Name defaultSLA
Profile Name defaultProfile
No. of times executed 1
Min. Execute Time 7,200.613830 secs
Max. Execute Time 7,200.613830 secs
Avg. Execute Time 7,200.613888 secs
Stats Collection Type OPERATOR_STATS
LC RC Id PaId ExId Frag TDBName DOP Dispatches OperCPUTime EstRowsUsed ActRowsUsed ActDataUsed Details
5 . 6 . 0 0 EX_ROOT 1 2 8 0 0 0 72297143|0|0|11333|
3 4 5 6 0 0 EX_ONLJ 1 366 22,537 1.19382e+06 0 0
. . 4 5 0 0 EX_TRAF_VSBB_DELETE 1 181 166,885 1 183,118 0 TRAF_RSRVD_3:TRAFODION.SEABASE.IDX_TEST_DELETE|10496397|7195172250|0|
1 2 3 5 0 0 EX_ONLJ 1 368 49,313 1.19382e+06 184,938 10,726,404
. . 2 3 0 0 EX_TRAF_DELETE 1 182 71,645,451 1 184,938 10,726,404 TRAF_RSRVD_3:TRAFODION.SEABASE.TEST_DELETE|20713164|7166976921|0|
. . 1 3 0 0 EX_TRAF_SELECT 1 182 412,949 1.19382e+06 186,188 10,798,904 TRAF_RSRVD_3:TRAFODION.SEABASE.TEST_DELETE|20108412|112207|186368|
在新的版本中，执行计划有了变化，
LC RC OP OPERATOR OPT DESCRIPTION CARD
---- ---- ---- -------------------- -------- -------------------- ---------
5 . 6 root x 3.99E+005
3 4 5 nested_join 3.99E+005
. . 4 trafodion_vsbb_delet IDX_TEST_DELETE 1.00E+000
1 2 3 nested_anti_semi_joi 3.99E+005
. . 2 trafodion_vsbb_delet TEST_DELETE 1.00E+000
. . 1 trafodion_scan TEST_DELETE 3.99E+005
我们可以看到，现在对于主表的删除动作也变为了TRAFODION_VSBB_DELET，运行时的统计信息如下，执行时长为21秒。
>>get statistics for qid current default;
Qid MXID11000014915212447930791902416000000000206U3333302T000_109___SQLCI_DML_LAST__
Compile Start Time 2020/02/08 22:16:13.997512
Compile End Time 2020/02/08 22:16:14.012970
Compile Elapsed Time 0:00:00.015458
Execute Start Time 2020/02/08 22:16:14.014781
Execute End Time 2020/02/08 22:16:35.745718
Execute Elapsed Time 0:00:21.730937
State DEALLOCATED
Rows Affected 999,900
SQL Error Code 0
Stats Error Code 0
Query Type SQL_DELETE_NON_UNIQUE
Sub Query Type SQL_STMT_NA
Estimated Accessed Rows 0
Estimated Used Rows 0
Parent Qid NONE
Parent Query System NONE
Child Qid NONE
Number of SQL Processes 1
Number of Cpus 1
Transaction Id 72339069014638598
Source String delete from test_delete where a>100;
SQL Source Length 36
Rows Returned 0
First Row Returned Time -1
Last Error before AQR 0
Number of AQR retries 0
Delay before AQR 0
No. of times reclaimed 0
Cancel Time -1
Last Suspend Time -1
Query hash 0
SLA Name defaultSLA
Profile Name defaultProfile
No. of times executed 1
Min. Execute Time 21.730937 secs
Max. Execute Time 21.730937 secs
Avg. Execute Time 21.730936 secs
Stats Collection Type OPERATOR_STATS
LC RC Id PaId ExId Frag TDBName DOP Dispatches OperCPUTime EstRowsUsed ActRowsUsed ActDataUsed Details
5 . 6 . 0 0 EX_ROOT 1 1 1 0 0 0 4252678|0|0|10469|
3 4 5 6 0 0 EX_ONLJ 1 2,567 101,380 399960 0 0
. . 4 5 0 0 EX_TRAF_VSBB_DELETE 1 2,149 790,288 1 999,900 0 TRAF_RSRVD_3:TRAFODION.SEABASE.IDX_TEST_DELETE|56996256|20548235|0|
1 2 3 5 0 0 EX_ONLJ_ANTI_SEMI_JOIN 1 2,490 183,404 399960 999,900 57,994,200
. . 2 3 0 0 EX_TRAF_VSBB_DELETE 1 1,585 1,175,555 1 999,900 0 TRAF_RSRVD_3:TRAFODION.SEABASE.TEST_DELETE|5001456|13902261|0|
. . 1 3 0 0 EX_TRAF_SELECT 1 976 2,002,050 399960 999,900 57,994,200 TRAF_RSRVD_3:TRAFODION.SEABASE.TEST_DELETE|107989200|4402094|999900|
对比以上两个执行计划，我们看到还有一个区别，就是有一个nested_join被改为了nested_anti_semi_join，这是因为trafodion_vsbb_delet没有返回结果但trafodion_delete有返回，当nested_join在一边有返回结果另一边没有返回结果时就会走semi join，再由于这里的nested_join是SELECT与DELETE操作符的关联，类似于NOT EXISTS或NOT IN，因此变成anti semi join的方式了。
