I have a SQL Server Profiler trace and it's working for all commands.
But the profiler skips one record like below:
If you insert a large amount of data, for example more than 1 MB, into SQL database in one single operation, the chance are that SQL Profiler is going to skip this operation, leave all fields blank, and mark as “Trace Skipped Records”. Don’t worry. The operation is still inserted into database, and only SQL Profiler skips the operation.
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The tkprof utility generates the trace file with three types of information which are Parse, Execute and Fetch. Could you please explain what is the difference between these three? What will be counted as Parse and Execute and Fetch?
Thanks in advance for your help.
When you issue a SQL statement, Oracle:
Parses your SQL statement. That means Oracle analyzes the correctness of the syntax, checks the access rights, and creates the execution plan (or takes it from the cache).
Actually executes your SQL statement.
For SELECT statements, Oracle fetches the rows returned by your query. (For INSERT, DELETE, and UPDATE Oracle fetches nothing).
The numbers of these operations is written in the trace.
If we are talking about the performance tuning, the idea is to parse SQL statements once and then keep them in cache, execute them when you need and do not close cursors if you will need them again to reduce number of fetches.
What is Plan hash value in Oracle ? Does this imply anything related to time of execution of a query ? How do I find execution time of a query in Oracle ?
There are 3 views that show SQL statements that ran in your SGA.
V$SQL shows stats and is updated every 5 seconds.
V$SQLAREA shows parsed statements in memory, ready to execute.
V$SQLSTATS has greater retention than V$SQL.
So if you look in V$SQL you will see every statement has a unique SQL ID. When the statement is parsed, oracle generates an explain plan for the SQL and then associates that plan with a hash value which is a unique value for that plan. Certain factors can cause the plan to change, making it execute better or worse. Then you will get a new plan and a new hash value for that plan.
To see the history of this, look at view DBA_HIST_SQL_PLAN.
There is a lot more theory around explain plans and how to optimize SQL statements, and how to give them profiles and baselines, but I hope this gives you an idea of the basics.
I've got a Oracle Insert query that runs and it has been busy for almost 24 hours.
The SELECT part of the statement had a cost of 211M.
Now I've updated the statistics on the source tables and the cost has came down significantly to 2M.
Should I stop and restart my INSERT statement, or will the new updated statistics automatically have an effect and start speeding up the performance?
I'm using Oracle 11g.
Should I stop and restart my INSERT statement, or will the new updated statistics automatically have an effect and start speeding up the performance?
New statistics will be used the next time Oracle parses them.
So, optimizer cannot update the execution plan based on the stats gathered at run time, since the query is already parsed and the execution plan has already been chosen.
What you can expect from 12c optimizer is, adaptive dynamic execution. It has the ability to adapt the plan at run time based on actual execution statistics. You can read more about it here http://docs.oracle.com/database/121/TGSQL/tgsql_optcncpt.htm
In Db trace, there is a query taking long time.Can some one explain what it means.Seems this is very generic oracle query and not involved with my custom tables.
select condition from cdef$ where rowid=:1;
Found the same query in multiple places in trc files(DB trace) and one among all have huge amount of elapsed time. So, what will be the solution to avoid taking such a long time. Am using 11g version oracle.
You're right, that is an example of Oracle's recursive SQL, the statements it runs against the data dictionary to support our application SQL. That particular statement is the query Oracle runs to get the Search Condition of a CHECK constraint. If you are inserting or updating rows in tables with check constraints you will see it a lot.
The actual statement shouldn't take too long to run, so it is unlikely to be the source of a performance problem. Unless you are running lots of insert statements with hard-coded values. Oracle will run that query every time it parses a fresh insert or update statement. That will get expensive if you're not using bind variables.
I have PL/SQL function that returns cursor that holds 28 columns and 8100 rows. When I execute that function from SQL Plus I got the results right away and in SQL Developer I'm running script that takes looong time (about 80 seconds). The same happen from Java code. When number of columns reduced to 2 then I got response in less than 4 seconds. Can someone explain what is going on in this case?
The easiest experiment to make is changing the "SQL Array Fetch Size" in SQL Developer, which defaults to 50. If you see results from bumping it to 500, there's the answer.
Interestingly, the default for the equivalent SQLPlus parameter is only 15, but as APC said, SQLPlus has the advantage of being native.
If changing "SQL Array Fetch Size" does not do anything, the next thing to look at is JDBC settings, which SQL Developer uses and SQL*Plus does not.
In addition to the good answers before mine...
SQL*PLus sends the data straight back to the screen as soon as the first rows are returned whereas SQL Developer has to find the size of the resultset to return in advance of displaying records.
This might explain why there is a delay for SQL Developer especially if the resultset is large or takes a long time to fully return (e.g. if the execution path is complicated).