Vector clocks


Once of the concepts I found difficult initially when looking at non-relational systems is the concept of the vector clock.  Some databases – like Cassandra - use timestamps to work out which is the “latest” transaction. If there are two conflicting modifications to a column value, the one with the highest timestamp will be considered the most recent and the most correct.

Other Dynamo systems use a more complex mechanism known as a (more...)

On my way to Collaborate 2015

As I write this I’m at 35,000 ft (or so) on my way to yet another Collaborate.  This year I’ll be presenting two sessions and participating in one panel:

963: Writing to Lead
Monday, April 13  |  Banyan E, South Convention Center, Level 2
10:30 a.m. – 11:30 a.m.
Jonathan Gennick will be moderating a panel including myself, Bobby Curtis, Charles Kim, Darl Kuln and Michael Rosenblum.  We’ll be talking about how writing (more...)

Sakila sample schema in MongoDB

I wanted to do some experimenting with MongoDB, but I wasn’t really happy with any of the sample data I could find in the web.  So I decided that I would translate the MySQL “Sakila” schema into MongoDB collections as part of the learning process.   

For those that don’t know, Sakila is a MySQL sample schema that was published about 8 years ago.  It’s based on a DVD rental system.   OK, (more...)

Best practices for accessing Oracle from scala using JDBC

I’ve been looking for an excuse to muck about with scala for a while now.  So I thought i’d do a post similar to those I’ve done the past for .NET, python, perl and R.  Best practices for Java were included in my book Oracle Performance Survival Guide (but I’d be more than happy to post them if anyone asks).

One of the great things about scala is that it runs (more...)

Using SSD for a temp tablespace on Exadata

I seem to be getting a lot of surprising performance results lately on our X-2 quarter rack Exadata system, which is good – the result you don’t expect is the one that teaches you something new.

This time, I was looking at using a temporary tablespace based on flash disks (more...)

Can the Exadata Smart Flash Cache slow smart scans?

I’ve been doing some work on the Exadata Smart Flash Cache recently and came across a situation in which setting CELL_FLASH_CACHE to KEEP will significantly slow down smart scans on a table.

If we create a table with default settings, then the Exadata Smart Flash Cache (ESFC) will not be (more...)

Redo on SSD: effect of redo size (Exadata)

Of all the claims I make about SSD for Oracle databases, the one that generates the most debate is that placing redo logs on SSD is not likely to be effective.  I’ve published data to that effect in particular see  Using SSD for redo on Exadata - pt 2 (more...)

Exadata Write-back cache and free buffer waits

Prior to storage server software version (associated with Exadata X3), Exadata Smart Flash Cache was a “write-through” cache, meaning that write operations are applied both to the cache and to the underlying disk devices, but are not signalled as complete until the IO to the (more...)

Redo log sync time vs redo size

It’s been tough to find time to do actual performance research of late, but I have managed to get a test system prepared that will allow me to determine if Solid State disks offer some performance advantage over spinning disks when the redo entries are very large.   This is (more...)


When Steven and I wrote MySQL Stored Procedure programming our biggest reservation about the new stored procedure language was the lack of support for proper error handling.  The lack of the SIGNAL and RESIGNAL clauses prevented a programmer from raising an error that could be propagated throughout a call (more...)