First Journaling FS for Linux

wendyW writes "LinuxPR has the press release from Namesys, announcing the stable release of the journaling version of ReiserFS. According to the press release, journaling wound up making it even faster than it already was. "

Comments

Important, but likely not for DBMSes

[Christopher B. Brown]

I hate to take issue with a well-spoken posting, but journalling is not of primary usefulness for helping support High Availability RDBMS systems.

The main effect of journalling, the thing that is really important about it, is that it guarantees that metadata updates are kept consistent. That is, journalling is primarily supportive of making sure that filenames, directory structures, permissions, and such are kept consistent even when moderately catastrophic things happen.

This is a really good thing when supporting file serving activities, as that indeed tends to involve lots of manipulations of files as users shift them around.

I've been on the ReiserFS mailing list since '97; have been running a personal news spool on a small ReiserFS partition for probably 6 months. I can't tell for sure if the journalling now available is metadata-only, or if it also journals normal data updates. It looks rather more like metadata-only, which is useful for file-server work, but not so much for RDBMSes.

Databases behave in quite different ways from file servers in terms of the way they do file access.

If you look at most RDBMSes, they create a few files, and do lots of manipulations on top of them. Informix SE is a counterexample, basically using Informix C-ISAM underneath, but is unusual in that regard. If you look at the database partitions, you get one of two things:

• Partitions containing a few very large files.

  Note that for these, the metadata is very static which means that journalling of metadata is of relatively little importance.

• Partitions containing no filesystem, but rather raw data being managed by the RDBMS.

  Don't just believe me; I am not the ultimate authority on this. Transaction Processing : Concepts and Techniques is a rather definitive reference; it discusses methods of managing transactions in the context of database management systems, and goes into considerable detail discussing transaction logging, which bears striking (and not merely coincidental) resemblance to journalling.

  The critical point here is that it is the database manager that wants to manage the logging/journalling; Oracle and Sybase and IBM and Informix will be loathe to pass on responsibility for this to Hans Reiser, wonderful guy though he is.

Conclusions

1. Sorry, I have to disagree with you on ReiserFS being of fundamental importance to those doing serious database work.

   What will be of fundamental importance will be when Stephen Tweedy's Raw Device Support gets integrated into the "production" kernels. That is what Oracle is looking for (consider: Oracle has pumped some funds into RHAT, and RHAT is paying Stephen Tweedie... Could there be some connection?)

2. Journalling IS important for sorts of applications that manipulate lots of files, which includes things like dynamic web serving and file serving.

   Even if this isn't such a boon to those doing serious RDBMS work, it can still be a boon to lots of other folks...