Oracle

Jonathan Lewis's picture

Parallel Execution

This is another little reference list I should have created some time ago. It covers a series of posts on interpreting parallel execution plans and understanding where the work happens.

dbakevlar's picture

Re-Adding a Database to the AWR Warehouse Without Losing Historical Snapshots

There may be a reason that one needs to re-add a database to the AWR Warehouse.  This is a new opportunity for me to learn and offer assistance, but I’m working off the grid to figure out a solution.  Luckily, it’s just a matter of creating a new process from pre-existing code and processes.

kevinclosson's picture

Whitepaper: Oracle Database 11g and 12c Consolidation and Workload Scalability with EMC XtremIO 3.0

This is a just a quick blog post to direct readers to the best Oracle-related paper detailing the value EMC XtremIO brings to Oracle Database use cases.  I’ve been looking forward to the availability of this paper for quite some time as I supported (minimally, really) the EMC Global Solutions Engineering group in this effort. They really did a great job with this testing! I highly recommend this paper for readers who are interested in:

Jonathan Lewis's picture

Not Exists

This whole thing about “not exists” subqueries can run and run. In the previous episode I walked through some ideas of how the following query might perform depending on the data, the indexes, and the transformation that the optimizer might apply:

dbakevlar's picture

ASH Data and How Sizing an AWR Warehouse Can be Mitigated

When sizing the AWR Warehouse, one of my requirements is to have certain reports for a sampling of databases that will source the AWR Warehouse. This report provides me the right information to create the correct sizing requirements vs. any assumptions done with other choices.

Jonathan Lewis's picture

Not Exists

Another question on a seemingly simple “not exists” query has appeared on OTN just a few days after my last post about the construct. There are two little differences between the actual form of the two queries that make it worth repeating the analysis.

The first query was of the form:


select from big_table
where  not exists (select exact_matching_row from small table);

while the new query is of the form:

tanelpoder's picture

Advanced Oracle Troubleshooting Guide – Part 12: control file reads causing enq: SQ – contention waits?

Vishal Desai systematically troubleshooted an interesting case where the initial symptoms of the problem showed a spike of enq: SQ – contention waits, but he dug deeper – and found the root cause to be quite different. He followed the blockers of waiting sessions manually to reach the root cause – and also used my @ash/ash_wait_chains.sql and @ash/event_hist.sql scripts to extract the same information more conveniently (note that he had modified the scripts to take AWR snap_ids as time range parameters instead of the usual date/timestamp):

marco's picture

Database landscape 2014 visualization

I saw this database landscape 2014 overview from “451 Research” with an very nice visualization…

Jonathan Lewis's picture

Golden Oldies

I’ve just been motivated to resurrect a couple of articles I wrote for DBAZine about 12 years ago on the topic of bitmap indexes. All three links point to Word 97 documents which I posted on my old website in September 2003. Despite their age they’re still surprisingly good.

Jonathan Lewis's picture

Manuals

From time to time I read a question (or, worse, an answer) on OTN and wonder how someone could have managed to misunderstand some fundamental feature of Oracle – and then, as I keep telling people everyone should do – I re-read the manuals and realise that that sometimes the manuals make it really easy to come to the wrong conclusion.

Having nothing exciting to do on the plane to Bucharest today, I decided it was time to read the Concepts manual again – 12c version – to remind myself of how much I’ve forgotten. Since I was reading the mobi version on an iPad mini I can’t quote page numbers, but at “location 9913 of 16157″ I found the following text in a sidebar:

“LGWR can write redo log entries to disk before a transaction commits. The redo entries become permanent only if the transaction later commits.”

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