Re: [Libguestfs] [PATCH nbdkit 0/2] Rewrite xz plugin as a filter.

Actually I think we are going to need to retain the block cache. It solves a slightly different problem from placing the cache filter on top (in fact both are useful). Let's say you have an XZ file with a 100,000 byte block size. Then reading two blocks at 0-1000 and 1000-2000 would result in reading and uncompressing a whole block twice. The block cache in the xz plugin/filter avoids this; the cache on top does not. Interesting factoid: www.mirrorsite.org rapidly throttles any connection that makes repeated range requests ... However if you open a new connection it is unaffected by the throttling on the existing connection (I thought it would throttle based on IP address). Anyway this, combined with the large block size in the Fedora Cloud image, makes xz + curl virtually unusable. I also think the new filter would be better if it made larger reads. The plugin makes 8K reads (BUFSIZ) which is likely reasonable for reading from a local file. But the overhead of reading from the curl plugin probably makes much larger reads sensible. I wonder if the filter can intuit a good block size to use somehow?