Last month we had annoying problems caused by stuck Oracle process holding locks and not releasing them. Every few days one process hangs with status “ACTIVE”
and “SQL*Net message from client”
In that state it holds locks and never releases them. As this is active OLTP database, new sessions arrive wanting those locked resources but they could not get them. So after some time you get lots of waiters and if you don’t react quickly maximum number of processes could be reached. Then your database refuses new connections and you're system becomes unresponsive.
To complicate a problem little (more...)
This post could be interesting for those who are running active/passive failover clusters with Oracle Clusterware used for managing resources. In this case owner of the Clusterware installation is not the same as owner of the Oracle RDBMS installation. Among others, Clusterware is assigned for managing listener resource (start,stop,check).
Till 11g version listener logs were by default written in “$ORACLE_HOME/network/log”
but with 11g ADR (Automatic Diagnostic Repository) is introduced and location for listener log is changed. From 11g default location is “$ORACLE_BASE/diag/tnslsnr/<hostname>/listener_<dbname>/trace”
I’ve noticed that when you start listener as owner of Oracle RDBMS everything is working fine. Listener log (more...)
To create database link in another schema you must execute “create database link” logged in that schema or you can use workaround noted in this post:
How to Create a Database Link in Another User’s Schema
Neil Johnson wrote nice post on that subject and I’m using his method for creating database links in another user’s schema. So check it out - link is above.
Recently I had situation when I didn’t know password of the user on the local and remote database. But I had to create database link to compile some views and procedures.
In that case my (more...)
Yesterday colleague reported that he’s receiving wrong/odd result from query so we decided to examine closely what's happening. Query had more then 150 lines with inline view, group by clause, several outer joins, function, decodes and cases included. So the first step was to exclude all the stuff that wasn’t important for clearer diagnosis.
Environment: Oracle EE 220.127.116.11 on OEL 5.7
I will post shortened version of the query with fake table names and columns.
FROM table_1 r,
MAX ( DECODE (ri.c_name, 'SPACE', ri. (more...)
My DBA friend Dejan from Baze Podataka
database related site wrote post
about Oracle Bug 8943287 which reminded me how dangerous bug this is. I was completely unaware about this bug till few months ago.
For this blog post I want to write about “ORA-01578: ORACLE data block corrupted”
error and recovery. It is easy to recover from such error if you have RMAN backup - you, of course, have RMAN backup? (if not, create one) Even if you don’t have RMAN backup you can perform block recovery from OS based backups (datafile copies).
But can you perform block recovery (more...)
Two weeks ago a colleague DBA asked me what would be the best way to move SYSTEM tablespace with minimum downtime. There are several ways to perform that task and I will note what would be the best way in my opinion.
Messing with SYSTEM tablespace is always tricky so my goal would be minimum risk
and minimum downtime
My testing environment is 11gR1 database on Linux 32bit OS.
After quick search on that subject I’ve noticed that DBA’s are comfortable with moving/renaming other datafiles but SYSTEM or UNDO are making problems. Some tablespaces are essential and cannot be taken (more...)
I’ve just realized that I’m never fully satisfied after tuning queries with database links. Yes, I manage to improve performance significantly but I’m always missing some answers.
Case explained in this blog post is not exception also.
Source DB (Oracle 18.104.22.168 on Solaris 64bit)
Remote DB (Oracle 10.2.0.4 on Solaris 64bit)
(Table names and values are changed )
One of the developers reported me problem with this simple query:
To get better output click "View Source".
FROM tab1 cc,
WHERE cc.c_id = cfp.b_id
AND cc.code = (more...)