Oracle
I came across Oracle Coherence today. Seems like this is another approach to clustering than Oracle RAC. Seems like this is a way to scale middle tiers that require shared data without actually using the central database for that. On the other hand, looks like a clustering framework with rules defined by developers as opposed to Oracle RAC that is designed and built to be a black box delivering database services. Has anyone (yeah, I’m asking developers reading the blog) played with it and knows how it feels?
So you have followed the recipes to create a standby database, setup the database to switch logs automatically, and now, as with any good database, the space required to support the application grows and grows and grows. Eventually, using your monitoring software (in my case, Pythian’s avail or dailies), you get an alert suggesting that you will need to add additional space. In this case you are going to add a datafile to a tablespace, or add a brand new tablespace.
With this post, I’m starting a series about Oracle Block Change Tracking internals. The feature was introduced in Oracle 10 Release 1. I have already published my past presentations and the white paper about that. When I first started, I tried to dig at least something from Metalink, but the public notes contained no implementation details. What I extracted is some pieces of bug texts, and from there I concluded that fixed tables starting with X$KRC are most probably related to the BCT feature.
One of our clients had an ORA-1555 “snapshot too old” error two nights in a row. The quick and dirty fix would be to increase the retention_period and the potential size of the UNDO tablespace. I was looking at it together with Dave, my new team mate, and a small detail popped up right away — Query Duration=76584 — 21+ hours? I checked the retention period, and it was 2 hours, so the dirty fix would probably fail unless it’s very dirty — dumping undo retention to something like a day and blowing the UNDO tablespace, and still without guarantee that the query finish within a day.
I just want to raise a warning flag for DBAs using RMAN and flash recovery area in Oracle 10g. The lesson is, to avoid backing up archivelogs that have already been backed up when using plus archivelog in a backup script, make sure you enable RMAN optimization.
I chose to talk about a technique I used at a client’s site to report the topmost space-wasting objects in an Oracle database. I was looking for a way to detect these objects without having to run some expensive analyze statements or dbms_stats jobs. I found out that I can use the dbms_space package to do this. It worked very well for me and I’m sure lots of DBAs could use this technique too.
I first presented on Oracle 10g Block Change Tracking Internals at UKOUG 06 in Birmingham. It was very well received, but there were quite a few gaps in my knowledge, and I later discovered I was incorrect in some places. I’ve done some additional research, filled in the blanks and corrected in a few places. Download it here.
Looks like our blog has turned into a MySQL blog over this week, so I have to do something about it. Luckily, I have zillions of pending posts, so I’ll start with posting my presentations materials from this conference with my remarks on how it went in general.
We are assisting one of our clients with a data conversion project and have used a feature that I was surprised so few people knew about. It is the multi-table insert.
So, you just installed the Oracle 10g clusterware, you just ran root.sh and got an error, you just went to metalink Note:316583.1 or Note:387691.1 the given interface(s), “eth0″ is not public, public interfaces should be used to configure virtual IPs, it just failed, and now you are relying on Google to help you with what Metalink couldn’t. Well look no more, and here’s the solution.
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