From: Brad Hubbard Date: Thu, 15 Dec 2016 05:06:11 +0000 (+1000) Subject: doc/dev/osd_internals: add pgpool.rst X-Git-Tag: v11.1.1~47^2 X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=0f6be4c98cf26b0237cbfbe505c54eaedfe96351;p=ceph.git doc/dev/osd_internals: add pgpool.rst Signed-off-by: Brad Hubbard --- diff --git a/doc/dev/osd_internals/pgpool.rst b/doc/dev/osd_internals/pgpool.rst new file mode 100644 index 00000000000..45a252bd41f --- /dev/null +++ b/doc/dev/osd_internals/pgpool.rst @@ -0,0 +1,22 @@ +================== +PGPool +================== + +PGPool is a structure used to manage and update the status of removed +snapshots. It does this by maintaining two fields, cached_removed_snaps - the +current removed snap set and newly_removed_snaps - newly removed snaps in the +last epoch. In OSD::load_pgs the osd map is recovered from the pg's file store +and passed down to OSD::_get_pool where a PGPool object is initialised with the +map. + +With each new map we receive we call PGPool::update with the new map. In that +function we build a list of newly removed snaps +(pg_pool_t::build_removed_snaps) and merge that with our cached_removed_snaps. +This function included checks to make sure we only do this update when things +have changed or there has been a map gap. + +When we activate the pg we initialise the snap trim queue from +cached_removed_snaps and subtract the purged_snaps we have already purged +leaving us with the list of snaps that need to be trimmed. Trimming is later +performed asynchronously by the snap_trim_wq. +