Technorama

Running javadoc

vinayaknp — Fri, 27 Nov 2009 07:26:42 +0000

A quick handy reference to run javadocs from the command prompt:

% javadoc -d DOC_OUTPUT_DIR -sourcepath SOURCE_PATH -subpackages LIST_OF_PACKAGES separated by space

further ref: http://java.sun.com/j2se/1.4.2/docs/tooldocs/windows/javadoc.html

Vi: shortcut to replace word

vinayaknp — Thu, 19 Nov 2009 11:53:10 +0000

Go to the relevant word. To replace it type cw . Then enter the word. To replace the line from the cursor onwards type c$ and type the replacement.

To do the same change on multiple lines: Go to the position on the line where the change needs to be done. Then type . This will do the same replacement on the other line too

Catchback: Oracle Reg Expressions

vinayaknp — Fri, 09 Oct 2009 09:20:31 +0000

This is useful in cases where there is a need to replace only a part of a text and the before and after parts have to be retained.

Eg: http://mywebsite/page/1.htm has to be changed to http://yoururl/page/1.htm
select regexp_replace(URL, 'http://.*mywebsite(.*)','http://yoururl\1') from table

Using the (.*) to put the /page/1.htm is called catchback

Getting sql plans

vinayaknp — Sun, 12 Jul 2009 09:37:21 +0000

One of our sql procedure executions took a lot of time. But it was not being monitored when it was executing. So we need a way to figure out the execution plan for the query so we can pinpoint the problem. That is where the oracle history tables helped us
select * from dba_hist_sqltext where sql_text like '%TABLE_NAME%'
We knew the table name which was being accessed and so got the sql_id for the execution.

Next step was to get the execution plan:

select * from DBA_HIST_SQL_PLAN where sql_id = 'ABCDEF';

This showed us that the plan was using NESTED loops for execution.

The respective tables for run time monitoring are gv$sqltext and gv$sql_plan

Adding partitions to table

vinayaknp — Sat, 20 Jun 2009 12:49:38 +0000

Recently, we had performance issues in our SQL code and one of the ways we thought was to increase the number of partitions.

The way to do it is to give one alter table query for each partition. And also the best practice is to have the number of partitions as a power of 2. So we increased it from 8 to 16

ALTER TABLE table_name ADD PARTITION

This will add the partition and also recalculate the rows that need to be moved to the new partition.

Note: If there are Local indexes in the partitions, they are invalidated due to the new partitions added and they need to be made usable

ALTER TABLE list_customers MODIFY PARTITION asia REBUILD UNUSABLE LOCAL INDEXES;



Finding rows in table partition
vinayaknp — Sat, 20 Jun 2009 12:36:23 +0000

There are cases when we would need to know how many rows are present in each partition. This would help us in figuring out if the partition strategy is working fine or not


SELECT object_name, subobject_name, DBMS_MView.PMarker(dta.rowid), count(1)

from TABLE_NAME dta, all_objects ao

where ao.object_id =  DBMS_MView.PMarker(dta.rowid)

group by object_name, subobject_name, DBMS_MView.PMarker(dta.rowid)

order by 1,2 ;


       


Scheduler job monitoring
vinayaknp — Tue, 31 Mar 2009 10:14:02 +0000

Use the following query to take a look at oracle jobs that have run in a scheduler



    SELECT *

    FROM dba_scheduler_job_log

    WHERE TRUNC(log_date) = TRUNC(SYSDATE)

    AND job_name = ''


The following query helps to monitor currently running job status:


SELECT *

    FROM dba_scheduler_jobs

    WHERE job_name = '';


       


Oracle: locked objects
vinayaknp — Tue, 31 Mar 2009 10:10:41 +0000

The following query is helpful in figuring out if any objects have been locked during script execution:


select o.object_name, o.subobject_name, o.object_type, l.*

from gv$locked_object l, dba_objects o

where l.object_id = o.object_id;


Another query that can be used to figure out if there is a “deadlock” kind scenario in the database, i.e two or more processes vying for the same resources.. 


select    'SID ' || l1.sid ||' is blocking  ' || l2.sid blocking

from    v$lock l1, v$lock l2

where    l1.block =1 and l2.request > 0

and    l1.id1=l2.id1

and    l1.id2=l2.id2


       


Oracle: Query Rewrite settings
vinayaknp — Thu, 15 Jan 2009 14:08:46 +0000

Query rewrite is a very useful concept provided by Oracle so that queries on a table can be redirected to a Materialized view. I am not too familiar with this, so that will be the topic of another post. 
This is a quick post about the settings on the database to enable query rewrite. 
The following query helps in knowing the settings:



show parameter rewrite


In the results, the query_rewrite_enabled property must be true.
If it is false, query rewrite will not happen
To set it to true, use the following:



alter system set query_rewrite_enabled = TRUE ;


       


Table sizes in oracle
vinayaknp — Wed, 07 Jan 2009 12:15:51 +0000

To find out how much physical space a table occupies in Oracle Database, use the following query :



SELECT

   owner, table_name, segment_type,TRUNC(sum(bytes)/1024/1024) MEG

FROM

(SELECT segment_name table_name, owner, bytes, segment_type

 FROM dba_segments

 )

 WHERE owner in UPPER(SCHEMA_NAME)

GROUP BY table_name,segment_type, owner

HAVING SUM(bytes)/1024/1024 >= 10

ORDER BY SUM(bytes) desc;


This will return all the tables in the schema that occupy more than 10 MB of space.