Hi All, out of disk handler
I propose to enhance CouchDB to monitor disk occupancy and react automatically as free space becomes scarce. I've written a working prototype at: https://github.com/apache/couchdb/compare/main...out-of-disk-handler The `diskmon` application is part of Erlang/OTP and I suggest we use that as the base, since it supports all the platforms we support (and a few more). The patch reacts differently depending on whether it is database_dir or view_index_dir that runs out of space (of course they might both run out of space at the same time in the common case that the same device is used for both), namely; 1) Clustered database updates are prohibited (a 507 Insufficient Storage error is returned) 2) Background indexing is suspended (no new jobs will be started) 3) Querying a stale view is prohibited (a 507 Insufficient Storage error is returned) 4) Querying an up-to-date view is permitted The goal being to leave internal replication running (to avoid data loss) and compaction (as the only action that reduces disk occupancy). I can see adding an option to suspend _all_ writing at, say, 99% full, in order to avoid hitting actual end of disk, but have not coded this up in the branch so far. At the moment these all activate at once, which I think is not how we want to do this. I suggest that we have configuration options for; 1) a global toggle to activate the out of disk handler 2) a parameter for the used disk percentage of view_index_dir at which we suspend background indexing, defaulting to 80 3) a parameter for the used disk percentage of view_index_dir at which we refuse to update stale indexes, defaulting to 90 4) a parameter for the used disk percentage of database_dir at which we suspend writes, defaulting to 90. What do we all think? B.
