On Wednesday, June 12, 2024 12:25 PM, Dragan Simic wrote: >[Maybe this RFC deserves a "bump", so let me try.] >On 2024-04-08 18:29, Dragan Simic wrote: >> Hello all, >> >> A few days ago I've noticed a rather unusual issue, but still a >> realistic one. When automatic garbage collection kicks in, as a >> result of gc.auto >= 0, which is also the default, the local >> repository can be left in a rather strange state if there isn't enough >> free space available on the respective filesystem for writing the >> objects, etc. >> >> It might be a good idea to estimate the required amount of free >> filesystem space before starting the garbage collection, be it >> automatic or manual, and refuse the operation if there isn't enough >> free space available. >> >> As a note, the need_to_gc() function already does something a bit >> similar with the available system RAM. >> >> Any thoughts? I am not sure there is a good portable way of reliably doing this using OS APIs, particularly with virtual disks and shared file sets. An edge condition would be setting up a separate file set for content inside .git for massive repositories, so taking an estimate in the working index would not fix the above. It might be useful to add a configuration item like: gc.reserve = size # possibly with mb, kb, gb, tb, or some other suffix indicating how much space must be available to reserve prior to starting the operation. Then creating a file (with real content) inside .git (or .git/objects) with the reserved size. If the file cannot be constructed, gc gets suppressed. This can happen for more than size issue - permissions, for example. Note also that some file systems to not actually allocate the entire space just setting EOF, so that technique, while fast, will also not work portably. After the reserve works, it can be removed (and hopefully NFS will properly close it), providing a lock is put in place, followed by gc running. It might be useful to do this even on a non-auto gc. While this can be expensive (writing a block of stuff twice), it is safer this way. Just a thought. Randall.
