简单的删除查询。最好的指标是什么?
Simple delete query. What is the best index?
我们正在删除 table 中的大量行,如 所述,使用以下 SQL:
DELETE FROM MYTABLE
WHERE UPDT_TIMESTMP < v_Cut_Off_Date
AND ROWNUM <= C_MAX_DELETE;
我注意到 UPDT_TIMESTMP 可以为 NULL。该字段存储记录最后更新时间的 TIMESTAMP 值 在 初始创建之后。因此,如果更新时间为 NULL,我希望修改我的 SQL 以考虑创建时间。
DELETE FROM MYTABLE
WHERE NVL(UPDT_TIMESTMP, CRET_TIMESTMP) < v_Cut_Off_Date
AND ROWNUM <= C_MAX_DELETE;
我的偏好是不允许 NULL 并将 UPDT_TIMESTMP 列的值更新为 CRET_TIMESTMP 值,但这不是一个选项。
由于 table 会很大,一个月大约 2000 万条记录,每个月我都会删除一个月的旧数据,我想确保我可以快速找到记录以删除。
使用这个 原始 SQL,
DELETE FROM COMMRCL_CORE_CLM_DTL
WHERE UPDT_TIMESTMP < SYSDATE AND ROWNUM <= C_MAX_DELETE;
...没有索引,这是使用 Toad for Oracle 的查询计划:
Plan
DELETE STATEMENT ALL_ROWSCost: 2 Bytes: 41 Cardinality: 1
3 DELETE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
2 COUNT STOPKEY
1 TABLE ACCESS FULL TABLE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL Cost: 2 Bytes: 41 Cardinality: 1
添加了上次更新时间的索引:
CREATE INDEX FIN_IT_RPT.COMMRCL_CORE_CLM_DTL_UPDTM ON FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
(UPDT_TIMESTMP)
LOGGING
TABLESPACE USERS
PCTFREE 10
INITRANS 2
MAXTRANS 255
STORAGE (
MAXSIZE UNLIMITED
PCTINCREASE 0
BUFFER_POOL DEFAULT
FLASH_CACHE DEFAULT
CELL_FLASH_CACHE DEFAULT
)
NOPARALLEL;
在上次更新时间添加索引后的查询计划(使用索引)
Plan
DELETE STATEMENT ALL_ROWSCost: 0 Bytes: 41 Cardinality: 1
3 DELETE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
2 COUNT STOPKEY
1 INDEX RANGE SCAN INDEX FIN_IT_RPT.COMMRCL_CORE_CLM_DTL_UPDTM Cost: 0 Bytes: 41 Cardinality: 1
修改查询以在更新时间为 NULL 时使用创建日期
DELETE FROM COMMRCL_CORE_CLM_DTL
WHERE NVL(UPDT_TIMESTMP, CRET_TIMESTMP) < SYSDATE AND ROWNUM <= C_MAX_DELETE;
在创建时间上添加了单独的索引
CREATE INDEX FIN_IT_RPT.COMMRCL_CORE_CLM_DTL_CRET ON
FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
(CRET_TIMESTMP)
LOGGING
TABLESPACE USERS
PCTFREE 10
INITRANS 2
MAXTRANS 255
STORAGE (
MAXSIZE UNLIMITED
PCTINCREASE 0
BUFFER_POOL DEFAULT
FLASH_CACHE DEFAULT
CELL_FLASH_CACHE DEFAULT
)
NOPARALLEL;
添加 2 个单独的索引后检查查询计划。
DELETE STATEMENT ALL_ROWSCost: 2 Bytes: 54 Cardinality: 1
3 DELETE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
2 COUNT STOPKEY
1 TABLE ACCESS FULL TABLE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL Cost: 2 Bytes: 54 Cardinality: 1
问题:为什么两个索引都没有使用?
在同一索引中添加了一个包含 LAST UPDATE 和 CREATE TIME 列的新索引
CREATE INDEX FIN_IT_RPT.COMMRCL_CORE_CLM_DTL_UPDCRT ON FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
(UPDT_TIMESTMP, CRET_TIMESTMP)
LOGGING
TABLESPACE USERS
PCTFREE 10
INITRANS 2
MAXTRANS 255
STORAGE (
MAXSIZE UNLIMITED
PCTINCREASE 0
BUFFER_POOL DEFAULT
FLASH_CACHE DEFAULT
CELL_FLASH_CACHE DEFAULT
)
NOPARALLEL;
仍然没有使用索引。为什么?
Plan
DELETE STATEMENT ALL_ROWSCost: 2 Bytes: 54 Cardinality: 1
3 DELETE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
2 COUNT STOPKEY
1 TABLE ACCESS FULL TABLE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL Cost: 2 Bytes: 54 Cardinality: 1
我意识到 table 中没有太多数据会影响解释计划(我的数据很少。)我是否必须生成数百万行才能真正了解预期结果,或者我可以不这样做就得到一个大概的想法?
为什么上面的示例中没有使用索引,或者我误解了计划?
更新:
当我采纳 Mat 的建议将 DELETE 分解为两个更新时,第一个是创建日期:
DELETE FROM COMMRCL_CORE_CLM_DTL
WHERE UPDT_TIMESTMP < SYSDATE AND ROWNUM <= variable;
...更新日期的索引用于第一个
Plan
DELETE STATEMENT ALL_ROWSCost: 0 Bytes: 54 Cardinality: 1
3 DELETE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
2 COUNT STOPKEY
1 INDEX RANGE SCAN INDEX FIN_IT_RPT.COMMRCL_CORE_CLM_DTL_UPDCRT Cost: 0 Bytes: 54 Cardinality: 1
第二个 SQL...
DELETE FROM COMMRCL_CORE_CLM_DTL
WHERE UPDT_TIMESTMP IS NULL AND CRET_TIMESTMP < SYSDATE AND ROWNUM <= Variable;
使用了包含两列的索引:
Plan
DELETE STATEMENT ALL_ROWSCost: 0 Bytes: 54 Cardinality: 1
3 DELETE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
2 COUNT STOPKEY
1 INDEX RANGE SCAN INDEX FIN_IT_RPT.COMMRCL_CORE_CLM_DTL_UPDCRT Cost: 0 Bytes: 54 Cardinality: 1
第二种情况只需使用不带 NVL 的单独 DELETE 语句:
DELETE FROM MYTABLE
WHERE UPDT_TIMESTMP IS NULL AND CRET_TIMESTMP < v_Cut_Off_Date
AND ROWNUM <= C_MAX_DELETE;
您可以使用 ... WHERE UPDT_TIMESTMP < v_Cut_Off_Date OR (UPDT_TIMESTMP IS NULL AND CRET_TIMESTMP < v_Cut_Off_Date) ...
将两个语句合并为一个
如果您只有少数记录 UPDT_TIMESTMP IS NULL
,请使用 MY_NVL(UPDT_TIMESTMP,CRET_TIMESTMP)
创建一个基于函数的索引,其中函数 MY_NVL
returns CRET_TIMESTMP for UPDT_TIMESTMP IS NULL 和 NULL for UPDT_TIMESTMP IS NOT NULL,那么 where 条件看起来像 ... WHERE UPDT_TIMESTMP < v_Cut_Off_Date OR MY_NVL(UPDT_TIMESTMP,CRET_TIMESTMP) < v_Cut_Off_Date ...
您也可以使用 NVL(UPDT_TIMESTMP, CRET_TIMESTMP)
尝试基于函数的索引(正如 David 最初提出的那样 - 抱歉,David,我还没有阅读您的评论)
我们正在删除 table 中的大量行,如
DELETE FROM MYTABLE
WHERE UPDT_TIMESTMP < v_Cut_Off_Date
AND ROWNUM <= C_MAX_DELETE;
我注意到 UPDT_TIMESTMP 可以为 NULL。该字段存储记录最后更新时间的 TIMESTAMP 值 在 初始创建之后。因此,如果更新时间为 NULL,我希望修改我的 SQL 以考虑创建时间。
DELETE FROM MYTABLE
WHERE NVL(UPDT_TIMESTMP, CRET_TIMESTMP) < v_Cut_Off_Date
AND ROWNUM <= C_MAX_DELETE;
我的偏好是不允许 NULL 并将 UPDT_TIMESTMP 列的值更新为 CRET_TIMESTMP 值,但这不是一个选项。
由于 table 会很大,一个月大约 2000 万条记录,每个月我都会删除一个月的旧数据,我想确保我可以快速找到记录以删除。
使用这个 原始 SQL,
DELETE FROM COMMRCL_CORE_CLM_DTL
WHERE UPDT_TIMESTMP < SYSDATE AND ROWNUM <= C_MAX_DELETE;
...没有索引,这是使用 Toad for Oracle 的查询计划:
Plan
DELETE STATEMENT ALL_ROWSCost: 2 Bytes: 41 Cardinality: 1
3 DELETE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
2 COUNT STOPKEY
1 TABLE ACCESS FULL TABLE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL Cost: 2 Bytes: 41 Cardinality: 1
添加了上次更新时间的索引:
CREATE INDEX FIN_IT_RPT.COMMRCL_CORE_CLM_DTL_UPDTM ON FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
(UPDT_TIMESTMP)
LOGGING
TABLESPACE USERS
PCTFREE 10
INITRANS 2
MAXTRANS 255
STORAGE (
MAXSIZE UNLIMITED
PCTINCREASE 0
BUFFER_POOL DEFAULT
FLASH_CACHE DEFAULT
CELL_FLASH_CACHE DEFAULT
)
NOPARALLEL;
在上次更新时间添加索引后的查询计划(使用索引)
Plan
DELETE STATEMENT ALL_ROWSCost: 0 Bytes: 41 Cardinality: 1
3 DELETE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
2 COUNT STOPKEY
1 INDEX RANGE SCAN INDEX FIN_IT_RPT.COMMRCL_CORE_CLM_DTL_UPDTM Cost: 0 Bytes: 41 Cardinality: 1
修改查询以在更新时间为 NULL 时使用创建日期
DELETE FROM COMMRCL_CORE_CLM_DTL
WHERE NVL(UPDT_TIMESTMP, CRET_TIMESTMP) < SYSDATE AND ROWNUM <= C_MAX_DELETE;
在创建时间上添加了单独的索引
CREATE INDEX FIN_IT_RPT.COMMRCL_CORE_CLM_DTL_CRET ON
FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
(CRET_TIMESTMP)
LOGGING
TABLESPACE USERS
PCTFREE 10
INITRANS 2
MAXTRANS 255
STORAGE (
MAXSIZE UNLIMITED
PCTINCREASE 0
BUFFER_POOL DEFAULT
FLASH_CACHE DEFAULT
CELL_FLASH_CACHE DEFAULT
)
NOPARALLEL;
添加 2 个单独的索引后检查查询计划。
DELETE STATEMENT ALL_ROWSCost: 2 Bytes: 54 Cardinality: 1
3 DELETE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
2 COUNT STOPKEY
1 TABLE ACCESS FULL TABLE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL Cost: 2 Bytes: 54 Cardinality: 1
问题:为什么两个索引都没有使用?
在同一索引中添加了一个包含 LAST UPDATE 和 CREATE TIME 列的新索引
CREATE INDEX FIN_IT_RPT.COMMRCL_CORE_CLM_DTL_UPDCRT ON FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
(UPDT_TIMESTMP, CRET_TIMESTMP)
LOGGING
TABLESPACE USERS
PCTFREE 10
INITRANS 2
MAXTRANS 255
STORAGE (
MAXSIZE UNLIMITED
PCTINCREASE 0
BUFFER_POOL DEFAULT
FLASH_CACHE DEFAULT
CELL_FLASH_CACHE DEFAULT
)
NOPARALLEL;
仍然没有使用索引。为什么?
Plan
DELETE STATEMENT ALL_ROWSCost: 2 Bytes: 54 Cardinality: 1
3 DELETE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
2 COUNT STOPKEY
1 TABLE ACCESS FULL TABLE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL Cost: 2 Bytes: 54 Cardinality: 1
我意识到 table 中没有太多数据会影响解释计划(我的数据很少。)我是否必须生成数百万行才能真正了解预期结果,或者我可以不这样做就得到一个大概的想法?
为什么上面的示例中没有使用索引,或者我误解了计划?
更新:
当我采纳 Mat 的建议将 DELETE 分解为两个更新时,第一个是创建日期:
DELETE FROM COMMRCL_CORE_CLM_DTL
WHERE UPDT_TIMESTMP < SYSDATE AND ROWNUM <= variable;
...更新日期的索引用于第一个
Plan
DELETE STATEMENT ALL_ROWSCost: 0 Bytes: 54 Cardinality: 1
3 DELETE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
2 COUNT STOPKEY
1 INDEX RANGE SCAN INDEX FIN_IT_RPT.COMMRCL_CORE_CLM_DTL_UPDCRT Cost: 0 Bytes: 54 Cardinality: 1
第二个 SQL...
DELETE FROM COMMRCL_CORE_CLM_DTL
WHERE UPDT_TIMESTMP IS NULL AND CRET_TIMESTMP < SYSDATE AND ROWNUM <= Variable;
使用了包含两列的索引:
Plan
DELETE STATEMENT ALL_ROWSCost: 0 Bytes: 54 Cardinality: 1
3 DELETE FIN_IT_RPT.COMMRCL_CORE_CLM_DTL
2 COUNT STOPKEY
1 INDEX RANGE SCAN INDEX FIN_IT_RPT.COMMRCL_CORE_CLM_DTL_UPDCRT Cost: 0 Bytes: 54 Cardinality: 1
第二种情况只需使用不带 NVL 的单独 DELETE 语句:
DELETE FROM MYTABLE
WHERE UPDT_TIMESTMP IS NULL AND CRET_TIMESTMP < v_Cut_Off_Date
AND ROWNUM <= C_MAX_DELETE;
您可以使用 ... WHERE UPDT_TIMESTMP < v_Cut_Off_Date OR (UPDT_TIMESTMP IS NULL AND CRET_TIMESTMP < v_Cut_Off_Date) ...
如果您只有少数记录 UPDT_TIMESTMP IS NULL
,请使用 MY_NVL(UPDT_TIMESTMP,CRET_TIMESTMP)
创建一个基于函数的索引,其中函数 MY_NVL
returns CRET_TIMESTMP for UPDT_TIMESTMP IS NULL 和 NULL for UPDT_TIMESTMP IS NOT NULL,那么 where 条件看起来像 ... WHERE UPDT_TIMESTMP < v_Cut_Off_Date OR MY_NVL(UPDT_TIMESTMP,CRET_TIMESTMP) < v_Cut_Off_Date ...
您也可以使用 NVL(UPDT_TIMESTMP, CRET_TIMESTMP)
尝试基于函数的索引(正如 David 最初提出的那样 - 抱歉,David,我还没有阅读您的评论)