[英]DELETE query performance
Original query 原始查询
delete B from
TABLE_BASE B ,
TABLE_INC I
where B.ID = I.IDID and B.NUM = I.NUM;
Performanace stats for above query 以上查询的性能统计数据
+-------------------+---------+-----------+
| Response Time | SumCPU | ImpactCPU |
+-------------------+---------+-----------+
| 00:05:29.190000 | 2852 | 319672 |
+-------------------+---------+-----------+
Optimized Query 1 优化查询1
DEL FROM TABLE_BASE WHERE (ID, NUM) IN
(SELECT ID, NUM FROM TABLE_INC);
Stats for above query 以上查询的统计信息
+-----------------+--------+-----------+
| QryRespTime | SumCPU | ImpactCPU |
+-----------------+--------+-----------+
| 00:00:00.570000 | 15.42 | 49.92 |
+-----------------+--------+-----------+
Optimized Query 2 优化查询2
DELETE FROM TABLE_BASE B WHERE EXISTS
(SELECT * FROM TABLE_INC I WHERE B.ID = I.ID AND B.NUM = I.NUM);
Stats for above query 以上查询的统计信息
+-----------------+--------+-----------+
| QryRespTime | SumCPU | ImpactCPU |
+-----------------+--------+-----------+
| 00:00:00.400000 | 11.96 | 44.93 |
+-----------------+--------+-----------+
My question - 我的问题 -
SELECT *
I am using SELECT ID,NUM
reducing to only two columns but Query 2 is showing better results. 我觉得查询1是理想的,因为我使用SELECT ID,NUM
而不是SELECT *
SELECT ID,NUM
只减少到两列但查询2显示更好的结果。 QUERY 1
This query is optimized using type 2 profile T2_Linux64, profileid 21.
1) First, we lock TEMP_DB.TABLE_BASE for write on a
reserved RowHash to prevent global deadlock.
2) Next, we lock TEMP_DB_T.TABLE_INC for access, and we
lock TEMP_DB.TABLE_BASE for write.
3) We execute the following steps in parallel.
1) We do an all-AMPs RETRIEVE step from
TEMP_DB.TABLE_BASE by way of an all-rows scan
with no residual conditions into Spool 2 (all_amps), which is
redistributed by the hash code of (
TEMP_DB.TABLE_BASE.NUM,
TEMP_DB.TABLE_BASE.ID) to all AMPs. Then
we do a SORT to order Spool 2 by row hash. The size of Spool
2 is estimated with low confidence to be 168,480 rows (
5,054,400 bytes). The estimated time for this step is 0.03
seconds.
2) We do an all-AMPs RETRIEVE step from
TEMP_DB_T.TABLE_INC by way of an all-rows scan
with no residual conditions into Spool 3 (all_amps), which is
redistributed by the hash code of (
TEMP_DB_T.TABLE_INC.NUM,
TEMP_DB_T.TABLE_INC.ID) to all AMPs. Then
we do a SORT to order Spool 3 by row hash and the sort key in
spool field1 eliminating duplicate rows. The size of Spool 3
is estimated with high confidence to be 5,640 rows (310,200
bytes). The estimated time for this step is 0.03 seconds.
4) We do an all-AMPs JOIN step from Spool 2 (Last Use) by way of an
all-rows scan, which is joined to Spool 3 (Last Use) by way of an
all-rows scan. Spool 2 and Spool 3 are joined using an inclusion
merge join, with a join condition of ("(ID = ID) AND
(NUM = NUM)"). The result goes into Spool 1 (all_amps),
which is redistributed by the hash code of (
TEMP_DB.TABLE_BASE.ROWID) to all AMPs. Then we do
a SORT to order Spool 1 by row hash and the sort key in spool
field1 eliminating duplicate rows. The size of Spool 1 is
estimated with no confidence to be 168,480 rows (3,032,640 bytes).
The estimated time for this step is 1.32 seconds.
5) We do an all-AMPs MERGE DELETE to
TEMP_DB.TABLE_BASE from Spool 1 (Last Use) via the
row id. The size is estimated with no confidence to be 168,480
rows. The estimated time for this step is 42.95 seconds.
6) We spoil the parser's dictionary cache for the table.
7) Finally, we send out an END TRANSACTION step to all AMPs involved
in processing the request.
-> No rows are returned to the user as the result of statement 1.
QUERY 2 EXPLAIN PLAN
This query is optimized using type 2 profile T2_Linux64, profileid 21.
1) First, we lock TEMP_DB.TABLE_BASE for write on a reserved RowHash to
prevent global deadlock.
2) Next, we lock TEMP_DB_T.TABLE_INC for access, and we
lock TEMP_DB.TABLE_BASE for write.
3) We execute the following steps in parallel.
1) We do an all-AMPs RETRIEVE step from TEMP_DB.TABLE_BASE by way of
an all-rows scan with no residual conditions into Spool 2
(all_amps), which is redistributed by the hash code of (
TEMP_DB.TABLE_BASE.NUM, TEMP_DB.TABLE_BASE.ID) to all AMPs.
Then we do a SORT to order Spool 2 by row hash. The size of
Spool 2 is estimated with low confidence to be 168,480 rows (
5,054,400 bytes). The estimated time for this step is 0.03
seconds.
2) We do an all-AMPs RETRIEVE step from
TEMP_DB_T.TABLE_INC by way of an all-rows scan
with no residual conditions into Spool 3 (all_amps), which is
redistributed by the hash code of (
TEMP_DB_T.TABLE_INC.NUM,
TEMP_DB_T.TABLE_INC.ID) to all AMPs. Then
we do a SORT to order Spool 3 by row hash and the sort key in
spool field1 eliminating duplicate rows. The size of Spool 3
is estimated with high confidence to be 5,640 rows (310,200
bytes). The estimated time for this step is 0.03 seconds.
4) We do an all-AMPs JOIN step from Spool 2 (Last Use) by way of an
all-rows scan, which is joined to Spool 3 (Last Use) by way of an
all-rows scan. Spool 2 and Spool 3 are joined using an inclusion
merge join, with a join condition of ("(NUM = NUM) AND
(ID = ID)"). The result goes into Spool 1 (all_amps), which
is redistributed by the hash code of (TEMP_DB.TABLE_BASE.ROWID) to all
AMPs. Then we do a SORT to order Spool 1 by row hash and the sort
key in spool field1 eliminating duplicate rows. The size of Spool
1 is estimated with no confidence to be 168,480 rows (3,032,640
bytes). The estimated time for this step is 1.32 seconds.
5) We do an all-AMPs MERGE DELETE to TEMP_DB.TABLE_BASE from Spool 1 (Last
Use) via the row id. The size is estimated with no confidence to
be 168,480 rows. The estimated time for this step is 42.95
seconds.
6) We spoil the parser's dictionary cache for the table.
7) Finally, we send out an END TRANSACTION step to all AMPs involved
in processing the request.
-> No rows are returned to the user as the result of statement 1.
For TABLE_BASE 对于TABLE_BASE
+----------------+----------+
| table_bytes | skewness |
+----------------+----------+
| 16842085888.00 | 22.78 |
+----------------+----------+
For TABLE_INC 对于TABLE_INC
+-------------+----------+
| table_bytes | skewness |
+-------------+----------+
| 5317120.00 | 44.52 |
+-------------+----------+
What's the relation between TABLE_BASE
and TABLE_INC
? TABLE_BASE
和TABLE_INC
之间的关系是什么?
If it's one-to-many Q1 probably creates a huge spool first while Q2&3 might apply DISTINCT
before the join. 如果它是一对多的Q1可能会首先创建一个巨大的假脱机,而Q2和3可能会在加入之前应用DISTINCT
。
Regarding IN
vs. EXISTS
there should be hardly any difference, did you check dbc.QryLogStepsV? 关于IN
与EXISTS
几乎没有任何区别,你检查了dbc.QryLogStepsV吗?
Edit: 编辑:
If (ID,Num)
is the PI of the target table rewriting to a MERGE DELETE should provide best performance: 如果(ID,Num)
是目标表的PI,则重写为MERGE DELETE应提供最佳性能:
MERGE INTO TABLE_BASE AS tgt
USING TABLE_INC AS src
ON src.ID = tgt.ID,
AND src.Num = tgt.Num
WHEN MATCHED
THE DELETE
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