I have an Oracle bind query that is extremely slow (about 2 minutes) when it executes in my C# program but runs very quickly in SQL Developer. It has two parameters that hit the tables index:
select t.Field1, t.Field2
from theTable t
where t.key1=:key1
and t.key2=:key2
Also, if I remove the bind variables and create dynamic sql, it runs just like it does in SQL Developer.
Any suggestion?
BTW, I'm using ODP.
If you are replacing the bind variables with static varibles in sql developer, then you're not really running the same test. Make sure you use the bind varibles, and if it's also slow you're just getting bit by a bad cached execution plan. Updating the stats on that table should resolve it.
However if you are actually using bind variables in sql developers then keep reading. The TLDR version is that parameters that ODP.net run under sometimes cause a slightly more pessimistic approach. Start with updating the stats, but have your dba capture the execution plan under both scenarios and compare to confirm.
I'm reposting my answer from here: https://stackoverflow.com/a/14712992/852208
I considered flagging yours as a duplicate but your title is a little more concise since it identifies the query does run fast in sql developer. I'll welcome advice on handling in another manner.
Adding the following to your config will send odp.net tracing info to a log file:
This will probably only be helpful if you can find a large gap in time. Chances are rows are actually coming in, just at a slower pace.
Try adding "enlist=false" to your connection string. I don't consider this a solution since it effecitively disables distributed transactions but it should help you isolate the issue. You can get a little bit more information from an oracle forumns post:
From an ODP perspective, all we can really point out is that the
behavior occurs when OCI_ATR_EXTERNAL_NAME and OCI_ATR_INTERNAL_NAME
are set on the underlying OCI connection (which is what happens when
distrib tx support is enabled).
I'd guess what you're not seeing is that the execution plan is actually different (meaning the actual performance hit is actually occuring on the server) between the odp.net call and the sql developer call. Have your dba trace the connection and obtain execution plans from both the odp.net call and the call straight from SQL Developer (or with the enlist=false parameter).
If you confirm different execution plans or if you want to take a preemptive shot in the dark, update the statistics on the related tables. In my case this corrected the issue, indicating that execution plan generation doesn't really follow different rules for the different types of connections but that the cost analysis is just slighly more pesimistic when a distributed transaction might be involved. Query hints to force an execution plan are also an option but only as a last resort.
Finally, it could be a network issue. If your odp.net install is using a fresh oracle home (which I would expect unless you did some post-install configuring) then the tnsnames.ora could be different. Host names in tnsnams might not be fully qualified, creating more delays resolving the server. I'd only expect the first attempt (and not subsequent attempts) to be slow in this case so I don't think it's the issue but I thought it should be mentioned.
Are the parameters bound to the correct data type in C#? Are the columns key1 and key2 numbers, but the parameters :key1 and :key2 are strings? If so, the query may return the correct results but will require implicit conversion. That implicit conversion is like using a function to_char(key1), which prevents an index from being used.
Please also check what is the number of rows returned by the query. If the number is big then possibly C# is fetching all rows and the other tool first pocket only. Fetching all rows may require many more disk reads in that case, which is slower. To check this try to run in SQL Developer:
SELECT COUNT(*) FROM (
select t.Field1, t.Field2
from theTable t
where t.key1=:key1
and t.key2=:key2
)
The above query should fetch the maximum number of database blocks.
Nice tool in such cases is tkprof utility which shows SQL execution plan which may be different in cases above (however it should not be).
It is also possible that you have accidentally connected to different databases. In such cases it is nice to compare results of queries.
Since you are raising "Bind is slow" I assume you have checked the SQL without binds and it was fast. In 99% using binds makes things better. Please check if query with constants will run fast. If yes than problem may be implicit conversion of key1 or key2 column (ex. t.key1 is a number and :key1 is a string).
Related
i'm struggeling with Performance in oracle. Situation is: Subsystem B has a dblink to master DB A. on System B a query completes after 15 seconds over dblink, db plan uses appropriate indexes.
If same query should fill a table in a stored procedure now, Oracle uses another plan with full scans. whatever i try (hints), i can't get rid of these full scans. that's horrible.
What can i do?
The Oracle Query Optimizer tries 2000 different possibilities and chooses the best one in normal situations. But if you think it choose wrong plan, You may suspect the following cases:
1- Your histograms which belongs to querying tables are deprecated.
2- Your indexes can not be used because of your faulty query.
3- You can use index hints to force the indexes to be used.
4- You can use SQL Advisor or run TKProf for performance analysis and decide what's wrong or what caused bad performance. Check network, Disk I/O values etc.
If you share your query we can give you more information.
Look like we are not taking same queries in two different conditions.
First case is Simple select over dblink & Second case is "insert as select over dblink".
can you please share two queries & execution plans here as You may have them handy. If its not possible to past queries due to security limitations, please past execution plans.
-Abhi
after many tries, I could create a new DB Plan with Enterprise Manager. now it's running perfect.
We had a performance issue in our production environment.
We identified that Oracle was executing queries using a Index which is not correct.
The queries have in their WHERE CLAUSE all the columns of the Primary Key (and nothing else).
After rebuilding of Index and Gather Statistics, Oracle started using the PK_INDEX. And the plan of execution indicated Index Unique Scan.
It worked fine for a while and then Oracle started using the Wrong Index again. The index that it uses now comprise of 2 Columns of which only 1 appears in the WHERE CLAUSE of the query. Now the plan of execution indicates INDEX RANGE SCAN and the system is very slow.
Please let me know how we could get to the root of this issue.
Try gathering stats again. If you get the expected execution plan then it means that the changes made to the table since the last stats gathering made oracle think the least favorite execution plan is better.
so, You'r question here is really "How can I maintain plan stability ?"
You have several options
Use hints in your query to indicate the exact access path.
Use
outlines
I personally don't like these two approaches because if your data will change in the future in such a manner that the execution plan should change, you'll get lousy performance.
So the third option (and my personal favorite) is
enable periodic statistics gathering. Oracle knows to spot the
changes and incrementally update relevant stats.
I have a vey huge query. It is rather large, so i will not post it here(it has 6 levels of nested queries with ordering and grouping). Query has 2 parameters that are passed to it via PreparedStatement.setString(index, value). When I execute my query through SQL Developer(replacing query parameters to actual values before it by hand) the query runs about 10 seconds and return approximately 15000 rows. But when I try to run it through java program using PreparedStament with varibales it fails with ORA-01652(unable to extend temp segment). I have tried to use simple Statement from java program - it works fine. Also when I use preparedStatement without variables(don't use setString(), but specify parameters by hand) it works fine too.
So, I suspect that problem is in PreparedStatemnt parameters.
How does the mechanism of that parameters work? Why simple statement works fine but prepared one fails?
You're probably running into issues with bind variable peeking.
For the same query, the best plan can be significantly different depending on the actual bind variables. In 10g, Oracle builds the execution plan based on the first set of bind variables used. 11g mostly fixed this problem with adaptive cursor sharing, a feature that creates multiple plans for different bind variables.
Here are some ideas for solving this problem:
Use literals This isn't always as bad as people assume. If the good version of your query runs in 10 seconds, the overhead of hard-parsing the query will be negligible. But you may need to be careful to avoid SQL injection.
Force a hard-parse There are a few ways to force Oracle to hard-parse every query. One method is to call DBMS_STATS with NO_INVALIDATE=>FALSE on one of the tables in the query.
Disable bind-variable peeking / hints You can do this by removing the relevant histograms, or using one of the parameters in the link provided by OldProgrammer. This will stabilize your plan, but will not necessarily pick the correct plan. You may also need to use hints to pick the right plan. But then you may not have the right plan for every combination of inputs.
Upgrade to 11g This may not be an option, but this issue is another good reason to start planning an upgrade.
I have an Oracle 9 database from which my Delphi 2006 application reads data into a TSimpleDataSet using a SQL statement like this one (in reality it is more complex, of course):
select * from myschema.mytable where ID in (1, 2, 4)
My applications starts up and executes this query quite often during the course of the day, each time with different values in the in clause.
My DBAs have notified me that this is creating execessive load on the database server, as the query is re-parsed on every run. They suggested to use bind variables instead of building the SQL statement on the client.
I am familiar with using parameterized queries in Delphi, but from the article linked to above I get the feeling that is not exactly what bind variables are. Also, I would need theses prepared statements to work across different runs of the application.
Is there a way to prepare a statement containing an in clause once in the database and then have it executed with different parameters passed in from a TSimpleDataSet so it won't need to be reparsed every time my application is run?
My answer is not directly related to Delphi, but this problem in general. Your problem is that of the variable-sized in-list. Tom Kyte of Oracle has some recommendations which you can use. Essentially, you are creating too many unique queries, causing the database to do a bunch of hard-parsing. This will spike the CPU consumption (and DBA blood pressures) unnecessarily.
By making your query static, it can get by with a soft-parse or perhaps no parse at all! The DB can then cache the execution plan, the DBAs can deal with a more "stable" SQL, and overall performance should be improved.
I have a report engine, performing PreparedStatements on Oracle 11, that is a highly prioritized task.
What I see is that first query invocation usually performs much much longer than the same query afterwards (query has different parameters and return different data).
I suppose this is due to hard parsing done by Oracle, on first query invocation.
I wonder, is there a way of hinting to Oracle, that this query is highly prioritized query which would be performed often, and which performance is critical, so it should remain in shared pool, no matter what?
I know that I can fix execution plan in Oracle 11, but I don't want to fix it, I want Oracle still to be able to change it, as system changes, all I want is to exclude query hard parsing.
Perhaps you should change your "I suppose..." into a "I tested and have determined..." :)
The query performance may be affected by more than just parsing; when it executes it has to fetch blocks from disk into the buffer cache - subsequent executions quite possibly are taking advantage of the blocks being found in memory and so are faster.
EDIT: to answer your immediate question - a workaround may be to have a job run periodically that parses the query but doesn't execute it. You might even be able to use this to determine whether parsing or fetching is the locus of the problem.
You can try pinning to shared pool using dbms_shared_pool.keep
But I would first make sure that you have an aging out problem first
Anton,
if your query is using bind variables it will be re-used. The cursor will be cached and as long as it is re-used, it will remain in the cursor cache. Make sure that it uses bind variables. This increases re-usability and scalability.
If you don't trust the rdbms you can pin it using dbms_shared_pool.keep.
See http://psoug.org/reference/dbms_shared_pool.html
You need to find your cursor in order to do so.
Normally there is an other problem that should be fixed.
Ronald.
http://ronr.blogspot.com