OraChat – Oracle DBAs

I have made a few comments in previous posts about the latch: library cache and playing with cursor parameters that can introduce surprises; Here is another one library cache tuning – A Real Case Study. Scenario : Users started complaining about very poor application performance, hung and incomplete transactions. Some severity one ticket for immediate [...]

Hanganalyze / Librarycache contention Last week I was called up to  help to resolve one of the production database hung issue. This totally screwed the database by all means  [ Database connections were hanging, Connections on the server using SQL*Plus as sysdba was also hanging, EM grid was spinning ] Dammn totally stuck …. you [...]

Application Tier: Forms Forms performance issues may arise when dead connection persists on the server and consuming the server resources. Enable the forms dead client connection can eliminate the dead connection. FORMS60_TIMEOUT=10 (recommended value and value specified in minutes) Do $ ps –ef| grep f60webmx and terminates f60webmx processes for dead clients. Enable Forms Abnormal [...]

AWR query to find load spikes select to_char(round(sub1.sample_time, ‘HH24′), ‘YYYY-MM-DD HH24:MI’) as sample_hour, round(avg(sub1.on_cpu),1) as cpu_avg, round(avg(sub1.waiting),1) as wait_avg, round(avg(sub1.active_sessions),1) as act_avg, round( (variance(sub1.active_sessions)/avg(sub1.active_sessions)),1) as act_var_mean from ( — sub1: one row per ASH/AWR sample observation select sample_id, sample_time, sum(decode(session_state, ‘ON CPU’, 1, 0))  as on_cpu, sum(decode(session_state, ‘WAITING’, 1, 0)) as waiting, count(*) as active_sessions [...]

Here are few silver bullets to use AWR for diagnosing performance issues ….. AWR – Automatic Workload Repository Detailed & comprehensive performance history Based on “snapshot” (time interval) Automatic Database Diagnostic Monitor (ADDM) About 79 DBA_HIST_* “tables” Defaults: Hourly snapshots Weekly retention (month is better) Overview of important AWR tables DBA_HIST_SNAPSHOT PK: SNAP_ID DBID, INSTANCE_NUMBER [...]

For any performance tuning issue, our strategy in diagnosing the problem is to take a “top-down” approach and follow the trail of highest CPU consumption down to the offending processes, and eventually the offending sessions and query. Verify CPU Consumption on the server is the first step any DBA should do for a top-down approach [...]

Excessive undo block shipment and contention for undo buffers I have seen this scenario in one my projects where  Oracle EBS workload is high. When a select statement needs to read a block with active transactions, it has to cleanout the block and undo the changes to create a CR version. If the active transactions [...]

Reversing the index key This is accomplished by executing the following SQL statement: ALTER INDEX <index_name> REBUILD REVERSE; A reverse key index will invert the bytes of the index key column, so that values originally stored in the same block may be spread across multiple index leaf blocks. That will reduce buffer busy contention especially [...]

Globally busy buffers due to contention for index leaf and branch blocks As we discussed in previous sessions, because of batch INSERT high concurrency could occur for a relatively small set of index leaf and branch blocks, where index keys are populated with monotonically ascending values.The symptoms are increased frequencies and wait times for a [...]

After running Gather Schema Statistics concurrent request with (LASTRUN) option to save only the history for last run, then run the concurrent request again for 2 times after that found that (FND_STATS_HIST) tables contains the history for all the 3 requests and it is not cleaned up to keep only last run. Sample steps to [...]

Unidirectional oracle streams setup from Source database Sup.world to Replicated database Rup.world Step 1)   Initialization parameter setup – Following init parameters need to be set. 1. global_names = true 2. job_queue_processes = 4 3. aq_tm_processes = 1 4. logmnr_max_persistent_sessions = 1 5. log_parallelism = 1 6. parallel_max_servers = 2 7. streams_pool_size = 200 min 8. [...]

Why audit the SYS user, when SYS is super user? Since we deal with critical and confidential data it becomes highly necessary to monitor even the SYS user for data integrity. Data integrity refers to the validity of data; meaning data is consistent and correct. As the need to derive meaningful information from large sets [...]