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Solved
Oracle query tuning help required
Posted on 2016-08-26
I have a document archive that is somewhat of a tuple table where we store keywords that pertain to the document in one table and the path to the document in another. This setup was created almost 15 yrs ago and I'd rather not make any monumental changes to it.
The lookups are extremely slow as you can see by the query and the table definitions below. I have added a numeric fd_cli_rid value on the filedirectory table which should make lookups much faster. So, if I switch to go through the filedirectory table to get the records required, how would I rewrite this query to return all rows?
The FILEDIRECTORY table is primarily used for versioning of files. It can poossiby point to a different path than the FILENAME keyword in FILEKEYPAIR.
The lookups are extremely slow as you can see by the query and the table definitions below. I have added a numeric fd_cli_rid value on the filedirectory table which should make lookups much faster. So, if I switch to go through the filedirectory table to get the records required, how would I rewrite this query to return all rows?
The FILEDIRECTORY table is primarily used for versioning of files. It can poossiby point to a different path than the FILENAME keyword in FILEKEYPAIR.
select /*+INDEX(filekeypair filekeypair2)*/ FD_RID, FKP_KEYWORD, FKP_VALUE, FD_FILENAME, FD_LASTMODIFIED from filekeypair,(
select distinct p.*, rownum rnum from (
select /*+INDEX(filedirectory filedirattrib_fd_rid)*/ FD_LASTMODIFIED,FD_RID,FD_FILENAME
from filedirectory,(select * from filekeypair where FKP_KEYWORD='CLI_RID') z
where z.FKP_FD_RID(+)=FD_RID
and FD_RID in (select /*+INDEX(B FILEKEYPAIR3)*/ b.FKP_FD_RID from filekeypair b
where (upper(b.FKP_KEYWORD) like upper('CLI_RID')||'%'
and upper(b.FKP_VALUE) like upper('1026697')||'%')
and (upper(b.FKP_KEYWORD) like upper('DISTRIBUTION')||'%'
and upper(b.FKP_VALUE) not like upper('INTERNAL')||'%'))
order by z.FKP_VALUE ASC ,FD_LASTMODIFIED ASC
) p where rownum<=100000
) where rnum>=1 and FKP_FD_RID=FD_RID order by rnum
CREATE TABLE FILEKEYPAIR
(
FKP_FD_RID NUMBER,
FKP_KEYWORD VARCHAR2(100 BYTE),
FKP_VALUE VARCHAR2(110 BYTE),
FKP_INSUSER VARCHAR2(100 BYTE),
FKP_INSDATE DATE,
FKP_DELUSER VARCHAR2(100 BYTE),
FKP_DELDATE DATE
)
CREATE TABLE FILEDIRECTORY
(
FD_RID NUMBER(9),
FD_FILENAME VARCHAR2(1000 BYTE),
FD_LASTMODIFIED DATE,
FD_EVE_RID NUMBER(9),
FD_DELETED DATE,
FD_OLD CHAR(1 BYTE),
FD_CLI_RID NUMBER
)
FD_RID FKP_KEYWORD FKP_VALUE FD_FILENAME FD_LASTMODIFIED
---------- ------------ ---------------------------- --------------------------- -------------------
5741874 CLI_RID 1026697 \NEWCCDESIGMEMO20150103.PDF 1/5/2015 7:19:16 AM
5741874 DESIG CC \NEWCCDESIGMEMO20150103.PDF 1/5/2015 7:19:16 AM
5741874 PRINT_DATE 20150105 \NEWCCDESIGMEMO20150103.PDF 1/5/2015 7:19:16 AM
5741874 FILENAME \NewCCDesigMemo20150103.pdf \NEWCCDESIGMEMO20150103.PDF 1/5/2015 7:19:16 AM
5741874 DOC_NAME New CC Desig Memo \NEWCCDESIGMEMO20150103.PDF 1/5/2015 7:19:16 AM
DOC_NAME FILENAME PRINT_DATE DESIG CLI_RID
------------------ --------------------------- ----------- ------- --------
New CC Desig Memo \NewCCDesigMemo20150103.pdf 20150105 CC 1026697
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9 Comments
Active today
Where to start? This query contains example of many of the things to avoid in SQL if you want good performance from Oracle.
1. The use of operators, like: "upper(b.FKP_KEYWORD)" on database columns in "where" clauses should always be avoided, since these prevent Oracle from using indexes on that column (unless you have function-based indexes that exactly match this syntax).
2. The nested queries (select ... from (select...(from select...))) can create performance problems, depending on the numbers of records returned by the inner queries and on the amount of memory in your server, since these intermediate result sets need to be buffered somewhere and evaluated without the benefit of indexes.
3. Outer joins, for example: "where z.FKP_FD_RID(+)=FD_RID", can add significant performance penalties.
4. Filters on rownum *ONLY* reduce the number of rows returned by the query, They do *NOT* reduce the number of rows that Oracle has to process internally before returning the requested number of rows to the application.
Basically, it looks to me like whoever designed this query (or this system?) was concerned about flexibility but either had no concern for, or was unaware of, the impact on performance when Oracle queries are written like this.
1. The use of operators, like: "upper(b.FKP_KEYWORD)" on database columns in "where" clauses should always be avoided, since these prevent Oracle from using indexes on that column (unless you have function-based indexes that exactly match this syntax).
2. The nested queries (select ... from (select...(from select...))) can create performance problems, depending on the numbers of records returned by the inner queries and on the amount of memory in your server, since these intermediate result sets need to be buffered somewhere and evaluated without the benefit of indexes.
3. Outer joins, for example: "where z.FKP_FD_RID(+)=FD_RID", can add significant performance penalties.
4. Filters on rownum *ONLY* reduce the number of rows returned by the query, They do *NOT* reduce the number of rows that Oracle has to process internally before returning the requested number of rows to the application.
Basically, it looks to me like whoever designed this query (or this system?) was concerned about flexibility but either had no concern for, or was unaware of, the impact on performance when Oracle queries are written like this.
Ok, do you have any suggestions on how to re-write it other than just dumping on the original author?
Active today
First: is the data in columns: FKP_KEYWORD and FKP_VALUE in table: filekeypair actually stored in mixed-case, or lower-case values, or inconsistently, or is it actually stored in all upper-case values already? If this data is actually all upper-case, then removing the "upper" conversions on these may help greatly. If this data is not stored consistently, then you may need to create function-based indexes on these columns that use the "upper" operator. If you don't have permission to add indexes, and the data is stored inconsistently, then it is difficult to query it efficiently.
Second: we have no idea how many rows are returned by your nested queries, and we have no idea how much RAM your server has and what your SGA size is. Without some more information from you on these topics, we don't know if we should change these or not.
Third: is the outer join actually needed? That is, if you remove the outer join do you get the same number of records returned?
Fourth: can you provide filters to help reduce the rows returned to the number (or close to the number) that is currently being limited by use of rownum?
Second: we have no idea how many rows are returned by your nested queries, and we have no idea how much RAM your server has and what your SGA size is. Without some more information from you on these topics, we don't know if we should change these or not.
Third: is the outer join actually needed? That is, if you remove the outer join do you get the same number of records returned?
Fourth: can you provide filters to help reduce the rows returned to the number (or close to the number) that is currently being limited by use of rownum?
1. It is mixed-case, FKP_KEYWORD is supposed to be all uppercase but people inserting the records sometimes write keywords that aren't.
2. It depends on the user's archive that is queried. One user has over 14,000 document, which equals over 90,000 rows, most users are a lot less than that.
3. I don't really know, I didn't write the query and the PL/SQL developer we have here doesn't know who wrote it, either.
4. I'm not sure why it is written that way so I can't really tell you. I do know that we filter out all reacords where
2. It depends on the user's archive that is queried. One user has over 14,000 document, which equals over 90,000 rows, most users are a lot less than that.
3. I don't really know, I didn't write the query and the PL/SQL developer we have here doesn't know who wrote it, either.
4. I'm not sure why it is written that way so I can't really tell you. I do know that we filter out all reacords where
FKP_KEYWORD='DISTRIBUTION' AND FKP_VALUE='INTERNAL'
Active 2 days ago
Please provide explain plan of current SQL.
Also it would be helpful if you can provide the columns ( with priority ) for indexes mentioned in hint.
Also if functional, please provide the function.
For example : inner sql
select /*+INDEX(B FILEKEYPAIR3)*/ b.FKP_FD_RID from filekeypair b
where (upper(b.FKP_KEYWORD) like upper('CLI_RID')||'%'
and upper(b.FKP_VALUE) like upper('1026697')||'%')
and (upper(b.FKP_KEYWORD) like upper('DISTRIBUTION')||'%'
and upper(b.FKP_VALUE) not like upper('INTERNAL')||'%'))
order by z.FKP_VALUE ASC ,FD_LASTMODIFIED ASC
1. All columns have upper clause, if index FILEKEYPAIR3 is not functional index it may be rather deteriorating the performance than helping you.
2. order by clause, SORTS are very heavy operations and since above mentioned inline SQL is passing value to IN clause, I find the sort in this particular situation unnecessary.
3. Depending on frequency , concurrent executions , load and capability of system, parallel hint can be used if there are FULL TABLE SCANS , that may speed up things a little bit. Although not a big fan myself but still it helps specially when FTS is inevitable and SQLs are running during less load and more of a reporting nature i.e. 1 or on-demand executions
Also it would be helpful if you can provide the columns ( with priority ) for indexes mentioned in hint.
Also if functional, please provide the function.
For example : inner sql
select /*+INDEX(B FILEKEYPAIR3)*/ b.FKP_FD_RID from filekeypair b
where (upper(b.FKP_KEYWORD) like upper('CLI_RID')||'%'
and upper(b.FKP_VALUE) like upper('1026697')||'%')
and (upper(b.FKP_KEYWORD) like upper('DISTRIBUTION')||'%'
and upper(b.FKP_VALUE) not like upper('INTERNAL')||'%'))
order by z.FKP_VALUE ASC ,FD_LASTMODIFIED ASC
1. All columns have upper clause, if index FILEKEYPAIR3 is not functional index it may be rather deteriorating the performance than helping you.
2. order by clause, SORTS are very heavy operations and since above mentioned inline SQL is passing value to IN clause, I find the sort in this particular situation unnecessary.
3. Depending on frequency , concurrent executions , load and capability of system, parallel hint can be used if there are FULL TABLE SCANS , that may speed up things a little bit. Although not a big fan myself but still it helps specially when FTS is inevitable and SQLs are running during less load and more of a reporting nature i.e. 1 or on-demand executions
Active today
1. If the application allows character data to be entered in mixed-case, then getting consistent, efficient reports based on that data is a challenge. Are you allowed to add function-based indexes? They could help significantly.
2. Are you OK with the one user with lots of records getting slow performance? Or, do you want this query to be efficient for all users? Is your inner query always based on these same three values, or are they just an example:
where (upper(b.FKP_KEYWORD) like upper('CLI_RID')||'%'
and upper(b.FKP_VALUE) like upper('1026697')||'%')
and (upper(b.FKP_KEYWORD) like upper('DISTRIBUTION')||'%'
3. You may not know if the outer join operator is required, or not, but we certainly don't know. And we can't test it. Only you have your data. Please test the query with, then without, the outer join operator to see if the results are the same, or different.
4. We also certainly cannot tell you why the limits on rownum are in your query. What we can tell you is that a limit on rownum does not help performance - it only limits the results that are returned to the user/application.
I also just noticed this syntax in your query: "select distinct p.*, rownum rnum ...". That is a problem. In my opinion, "select distinct" is rarely the best approach in Oracle queries. (This syntax may be common in SQL Server, and may even be a good idea there.) In Oracle, this forces the database to do a sort operation on the results to eliminate possible duplicates. This takes time, and can cause slow performance. Also, selecting rownum in an Oracle query at the same level as a sort, or "order by" is usually useless, since rownum gets assigned before the sort (so the sort can jumble the rownum values). I admit, that I've never tested rownum with "select distinct" at the same level of an Oracle query, but I would not expect consistent results from that combination. With your data, is the "distinct" required here? If you don't know, test it with and without, and let us know.
2. Are you OK with the one user with lots of records getting slow performance? Or, do you want this query to be efficient for all users? Is your inner query always based on these same three values, or are they just an example:
where (upper(b.FKP_KEYWORD) like upper('CLI_RID')||'%'
and upper(b.FKP_VALUE) like upper('1026697')||'%')
and (upper(b.FKP_KEYWORD) like upper('DISTRIBUTION')||'%'
3. You may not know if the outer join operator is required, or not, but we certainly don't know. And we can't test it. Only you have your data. Please test the query with, then without, the outer join operator to see if the results are the same, or different.
4. We also certainly cannot tell you why the limits on rownum are in your query. What we can tell you is that a limit on rownum does not help performance - it only limits the results that are returned to the user/application.
I also just noticed this syntax in your query: "select distinct p.*, rownum rnum ...". That is a problem. In my opinion, "select distinct" is rarely the best approach in Oracle queries. (This syntax may be common in SQL Server, and may even be a good idea there.) In Oracle, this forces the database to do a sort operation on the results to eliminate possible duplicates. This takes time, and can cause slow performance. Also, selecting rownum in an Oracle query at the same level as a sort, or "order by" is usually useless, since rownum gets assigned before the sort (so the sort can jumble the rownum values). I admit, that I've never tested rownum with "select distinct" at the same level of an Oracle query, but I would not expect consistent results from that combination. With your data, is the "distinct" required here? If you don't know, test it with and without, and let us know.
This query has been in use for a number of years. It is called from a .Net web service. It is built dynamically from input parameters that allow the user to filter the documents to be returned.
The rnum parameter allows them to query by pages. The CLI_RID value filters them to their own documents and when we have other filters, like DOC_NAME, the where clause gets dynamically created just like the CLI_RID where clause.
Table definitions:
Plan:
The rnum parameter allows them to query by pages. The CLI_RID value filters them to their own documents and when we have other filters, like DOC_NAME, the where clause gets dynamically created just like the CLI_RID where clause.
Table definitions:
// filekypair is forced view of filekeypairattib
CREATE TABLE CIC3.FILEKEYPAIRATTIB
(
FKP_FD_RID NUMBER,
FKP_KEYWORD VARCHAR2(100 BYTE),
FKP_VALUE VARCHAR2(110 BYTE),
FKP_INSUSER VARCHAR2(100 BYTE),
FKP_INSDATE DATE,
FKP_DELUSER VARCHAR2(100 BYTE),
FKP_DELDATE DATE
)
// filedirectory is forced view of filedirattrib
CREATE TABLE CIC3.FILEDIRATTRIB
(
FD_RID NUMBER(9),
FD_FILENAME VARCHAR2(1000 BYTE),
FD_LASTMODIFIED DATE,
FD_EVE_RID NUMBER(9),
FD_DELETED DATE,
FD_OLD CHAR(1 BYTE)
)
select /*+INDEX(filekeypair filekeypair2)*/ FD_RID, FKP_KEYWORD, FKP_VALUE, FD_FILENAME, FD_LASTMODIFIED from filekeypair,(
select distinct p.*, rownum rnum from (
select /*+INDEX(filedirectory filedirattrib_fd_rid)*/ FD_LASTMODIFIED,FD_RID,FD_FILENAME
from filedirectory,(select * from filekeypair where FKP_KEYWORD='CLI_RID') z
where z.FKP_FD_RID(+)=FD_RID
and FD_RID in (select /*+INDEX(B FILEKEYPAIR3)*/ b.FKP_FD_RID from filekeypair b
where (upper(b.FKP_KEYWORD) like upper('CLI_RID')||'%'
and upper(b.FKP_VALUE) like upper('1026697')||'%')
)
order by z.FKP_VALUE ASC ,FD_LASTMODIFIED ASC
) p where rownum<=100000
) where rnum>=1 and FKP_FD_RID=FD_RID order by rnum desc
Plan:
SELECT STATEMENT ALL_ROWSCost: 18 Bytes: 3,378 Cardinality: 6
17 SORT ORDER BY Cost: 18 Bytes: 3,378 Cardinality: 6
16 TABLE ACCESS BY INDEX ROWID TABLE CIC3.FILEKEYPAIRATTIB Cost: 4 Bytes: 198 Cardinality: 6
15 NESTED LOOPS Cost: 17 Bytes: 3,378 Cardinality: 6
13 VIEW CIC3. Cost: 13 Bytes: 530 Cardinality: 1
12 HASH UNIQUE Cost: 13 Bytes: 77 Cardinality: 1
11 COUNT STOPKEY
10 VIEW CIC3. Cost: 12 Bytes: 77 Cardinality: 1
9 SORT ORDER BY STOPKEY Cost: 12 Bytes: 143 Cardinality: 1
8 NESTED LOOPS OUTER Cost: 11 Bytes: 143 Cardinality: 1
5 NESTED LOOPS Cost: 7 Bytes: 110 Cardinality: 1
2 SORT UNIQUE Cost: 4 Bytes: 33 Cardinality: 1
1 INDEX RANGE SCAN INDEX CIC3.FILEKEYPAIR3 Cost: 4 Bytes: 33 Cardinality: 1
4 TABLE ACCESS BY INDEX ROWID TABLE CIC3.FILEDIRATTRIB Cost: 2 Bytes: 77 Cardinality: 1
3 INDEX UNIQUE SCAN INDEX (UNIQUE) CIC3.FILEDIRATTRIB_FD_RID Cost: 1 Cardinality: 1
7 TABLE ACCESS BY INDEX ROWID TABLE CIC3.FILEKEYPAIRATTIB Cost: 4 Bytes: 33 Cardinality: 1
6 INDEX RANGE SCAN INDEX CIC3.FILEKEYPAIR2 Cost: 3 Cardinality: 1
14 INDEX RANGE SCAN INDEX CIC3.FILEKEYPAIR2 Cost: 3 Cardinality: 6
CREATE INDEX CIC3.FILEKEYPAIR2 ON CIC3.FILEKEYPAIRATTIB
(FKP_FD_RID, FKP_KEYWORD, FKP_INSDATE)
CREATE UNIQUE INDEX CIC3.FILEDIRATTRIB_FD_RID ON CIC3.FILEDIRATTRIB
(FD_RID)
CREATE INDEX CIC3.FILEKEYPAIR3 ON CIC3.FILEKEYPAIRATTIB
(UPPER("FKP_VALUE"), UPPER("FKP_KEYWORD"), FKP_FD_RID)
You know, I think I'm going to rethink this. On a test DB, I restructured filedirattrib to have a FD_CLI_RID column and populated it with the FKP_VALUE for the FKP_KEYWORD 'CLI_RID' for records with the same FKP_FD_RID as FD_RID. and it made the new query much faster when going through filedirattrib.
This would be the plan:
This would be the plan:
Plan
SELECT STATEMENT ALL_ROWSCost: 248 Bytes: 40,817 Cardinality: 343
5 TABLE ACCESS BY INDEX ROWID TABLE CIC3.FILEKEYPAIRATTIB Cost: 3 Bytes: 216 Cardinality: 6
4 NESTED LOOPS Cost: 248 Bytes: 40,817 Cardinality: 343
2 TABLE ACCESS BY INDEX ROWID TABLE CIC3.FILEDIRATTRIB Cost: 63 Bytes: 5,146 Cardinality: 62
1 INDEX RANGE SCAN INDEX CIC3.FILEDIRATTRIB_CLI_RID Cost: 3 Cardinality: 62
3 INDEX RANGE SCAN INDEX CIC3.FILEKEYPAIR2 Cost: 2 Cardinality: 6
select d.FD_RID, k.FKP_KEYWORD, k.FKP_VALUE, d.FD_FILENAME, d.FD_LASTMODIFIED from filekeypair k
inner join FILEDIRATTRIB d on k.fkp_fd_rid = d.FD_RID
where d.fd_cli_rid = 1026697
Active today
"This query has been in use for a number of years."
OK, but that doesn't mean the application was well-designed for the current use, or for the current data volumes, or for running on an Oracle database.
"It is called from a .Net web service."
That may explain the "SQL Server-like" syntax that I see in this query.
"It is built dynamically from input parameters that allow the user to filter the documents to be returned."
Ouch! Oracle is optimized for static SQL statements that use bind variables, rather than "hard-coded" literal values in the "where" clauses. With static SQL statements, Oracle can parse them only once, then re-use them over and over with different bind variable values, each time. With dynamically-generated SQL statement that include "hard-coded" literal values in the "where" clauses, Oracle has to parse each one every time, to answer questions like:
1. Are the table names valid?
2. Are the column names valid?
3. Does the logged-in user have permission to query the tables?
4. Are there indexes available on these tables on columns that match the columns referenced in the "where" clauses, to help Oracle avoid reading all records in the tables?
5. Does the database have up-to-date statistics on the tables and indexes that indicate: how many rows they contain; how many blocks are these rows scattered across; how many distinct values do the columns and indexes contain; are the rows physically ordered similar to an index or not, etc.?
These parsing actions take time. Applications that force Oracle to "hard parse" every SQL statement will be slower than applications that allow Oracle to use its strengths.
"The rnum parameter allows them to query by pages."
OK, that may make sense to an application developer, but that is not what Oracle is optimized for.
OK, but that doesn't mean the application was well-designed for the current use, or for the current data volumes, or for running on an Oracle database.
"It is called from a .Net web service."
That may explain the "SQL Server-like" syntax that I see in this query.
"It is built dynamically from input parameters that allow the user to filter the documents to be returned."
Ouch! Oracle is optimized for static SQL statements that use bind variables, rather than "hard-coded" literal values in the "where" clauses. With static SQL statements, Oracle can parse them only once, then re-use them over and over with different bind variable values, each time. With dynamically-generated SQL statement that include "hard-coded" literal values in the "where" clauses, Oracle has to parse each one every time, to answer questions like:
1. Are the table names valid?
2. Are the column names valid?
3. Does the logged-in user have permission to query the tables?
4. Are there indexes available on these tables on columns that match the columns referenced in the "where" clauses, to help Oracle avoid reading all records in the tables?
5. Does the database have up-to-date statistics on the tables and indexes that indicate: how many rows they contain; how many blocks are these rows scattered across; how many distinct values do the columns and indexes contain; are the rows physically ordered similar to an index or not, etc.?
These parsing actions take time. Applications that force Oracle to "hard parse" every SQL statement will be slower than applications that allow Oracle to use its strengths.
"The rnum parameter allows them to query by pages."
OK, that may make sense to an application developer, but that is not what Oracle is optimized for.
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