Block Change Tracking Internals: X$ Tables Research

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.

21-hours Phantom SELECT Causing ORA-1555 ‘snapshot too old’

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.

‘plus archivelog’ and RMAN optimization

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.

What is Behind Pythian’s Growth and Market Success?

This is more of an essay than a blog post, but this subject comes up time and again, and since I tripped across this interesting blog post by Pedro Timóteo about why he has decided not to be a sysadmin any more, I thought now’s as good a time as any to comment on what I think is a significant industry trend in production engineering work.

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