Oracle parallel execution interview questions and answers. Baze podataka mysql, oracle, postgresql, ms sql server. Tuning parallel execution doug burns oracle and zx. From the report we see that 75% of the time was spent in parallel execution px deq credit. Execute reply, which oracle considers to be an idle event as i.
Snap id snap time sessions cursorssession begin snap. Data guard redo apply and media recovery best practices 10g. Working as an oracle database administrator, completed oracle 10g oca, preparing for ocp. For complete details on scheduling batch jobs in oracle, see dr. Developers and dbas get help from oracle experts on. Send blkd is not contributing towards db time, then. As an idle event, but only when processes are running parallel to serial this is not a event of great concern. The imported data is compared and analyzed to create a.
I heard that is some problem in oracle 10g and we need to use some hint to fix it. Parallel execution challenge its about time charles. The slaves and the qc use table queues for the communication. Test for msg 4,5x amount free buffer waits log file sequential read px deq credit. Parallel execution challenge its about time charles hoopers. Oracle wait analysis techniques oracle tips by burleson consulting. Send blkd is not contributing towards db time, then which other wait event could be the culprit. When utilizing temp tablespace groups, a dba can offer impressive performance increases by spreading the io across multiple files vs. Round robin and parallel forced to serial dba kevlar. Name wait class p1 p2 p3 alter rbs offline administrative alter system set dispatcher administrative waited aq deallocate wait confi. When processes are running parallel to parallel, i am. Table q normal means consumers slaves waiting for producer slaves for data px deq credit.
Load estimates of raw data are 145150 million rows per batch load size is 2628 gb per batch. Im running a 20 sql count batch job on a 4node rac cluster. Signal ack px deque wait in 9i statspack does not filter out all idle px wait event in the top 5 wait event section. Oracle waiting for dictionary redo my capture abort with memory issue.
Figure 1 and figure 2 show those major dimensions in awr and ash data of oracle 10g, which hold true for 11g. Px deq credit send blkd sfaturi oracle tips and tricks. Can you please explain about the db time now shown in statspack reports 10g. I only wanted feedback on the 3 events that i reported. One would think that when you have a multicpu server it should be pretty straightforward in oracle 10g to copy records from one table with lob column to another in parallel nologging using all available cpu power. Oracle parallel execution interview questions and answers such as what are restrictions and disadvantages of parallel execution, which parameters exist in relation to parallel execution, how are activation and degree of parallelism determined, how can. Tuning large oracle batch jobs oracle consulting, oracle. Computer implemented methods, programs and systems for displaying statistical data in a graphical user interface are provided. As i mentioned earlier, my current favorite way to set up parallelism in oracle is using. Sometimes the performance problem with parallel execution comes from the huge volume of messaging that can take place typified by wait event px deq credit.
After fixed issue, i restart capture and get state as waiting for dictionary redo. Master note parallel execution wait events oracle dbem. Im not the dba so i dont have access to all the physical specs. The join across 10 million to 20 million rows just shows the wait to 90%. Oracle tips by burleson consulting february 14, 2014. Master note parallel execution wait events doc id 1097154. As to the second question, as you dont provide any information about the physical layout of your database, and this particular datafile, the only recommendation would be to reduce the io by tuning statements. This tutorial explains the most important and frequently asked faqs oracle wait events interview questions and answers such as what is the connection between wait events and database performance, how can i access wait event information, what are idle events.
So it can happen that you see a px idle wait event in this section. Only somebody who constantly looks for ways to be offended would think that. This means he waits that the slaves finished to execute the sql statement and that they send the result of the query back to the qc. We use your linkedin profile and activity data to personalize ads and to show you more relevant ads. Tips to reduce waits for px deq credit send blkd at database level id 738464. Oracle sql wait events interview questions and answers. Us8156421b2 analysis of database performance reports for. Halim is an oracle certified ocp dba and ocp developer with extensive expertise in database design, development, tuning, sql, plsql, apex, rac, dg and scripting languages.
Hi all, in awr report, the top 5 event always is always px deq credit. The point being that io bottlenecks should be identified with io wait events and not bchr, but if an io bottleneck does happen, it is worth knowing if the buffer cache is supporting the io load sufficiently. The complete and the most recent version of this article can be viewed from my oracle support knowledge section. Table q normal, wait for credit send blocked, px deq credit. Rho remedies 5 oracle waits table for instance, a db file parallel read wait is considered a user io on any version of oracle. For the complete script downloads and more details on the concepts of this article, see my book oracle tuning. As tempfiles are utilized differently than datafiles.
Ask tom using rebuild parallel option on large table. Hi we have some performance issue on the oracle 10g while running batch, where the batch time for the critical path run varies from 9hrs 14hrs. Expert oracle take a closer look at the oracle database. I have gne through many documents on metalink, some pointing to it being a bug or something not right with the way some of the idle events in 10g in a class other. Fast refresh of materialized view too slow oracle database 10g enterprise edition release 10. The commonest error in the documentation is that px deq credit. Before oracle 10g this was also a buffer busy wait. Temp tablespace groups have received little press and less discussion since their introduction in oracle 10g. I looked in the various snapshots captured by the awr using addm and found most wait events are related to px, specially px deq credit. Removing credentials from a cloned ebs production database when cloning a production database instance of the oracle ebusiness suite ebs, all production account credentials should be cleared in the cloned copy of the database. Master note parallel execution wait events oracle dbem support. Parallel query tuning expert oracle rac performance.
I run all of my systems with it on as i find the value it provides far outweighs any overhead it might be percieved to have. Yes, as i suspected the first period with many more active sessions on average is showing a lot of time spent on the parallel executionrelated px deq credit. Parallel execution challenge its about time 8 07 2012. According to the method, baseline data is imported from a first report which corresponds to a troublefree period. However later on all the processes except one started to wait on px deq credit.