Hi Vladimir,

On Tue, Dec 27, 2011 at 11:04 PM, Vladimir Sedach vsedach@gmail.com wrote:

How often should a BKNR datastore be snapshot? I tried daily, but that is clearly too much.

In my deployed application, I snapshot once per day. This has not bothered me beyond the disk space usage, but eventually I came up with a cron job to automatically purge old snapshots.

Is there a criteria (# of transaction since last snapshot) that can be used to determine this programmatically?

The store itself has no mechanisms regarding that. I have pondered over various ideas how one could schedule snapshots in a more intelligent fashion - One was to measure and accumulate transaction execution time and snapshot whenever the execution time would exceed some threshold. Nothing like that ever went into code, though, as the nightly scheme never caused any problems for me. After all, even with my largest application that has some 700k objects, a restart only takes a minute or two, and happens only every few months when I need to do some maintenance.

Related to this, are snapshots linked to each other? Are old ones unneeded? Is it ok to delete them if they are?

They are completely independent and can be deleted at will. Only the current/ and blob-root/ directories are needed. Blobs are not automatically garbage collected, though, as they could be referenced in older snapshots and the store has no information regarding such references. The function bknr.datastore::delete-orphaned-blob-files can be used to remove all blob files that are not currently referenced from the store.

Let me know if you need further information.

Cheers, Hans