mirror of https://github.com/ceph/ceph
23 lines
1.0 KiB
ReStructuredText
23 lines
1.0 KiB
ReStructuredText
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==================
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PGPool
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==================
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PGPool is a structure used to manage and update the status of removed
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snapshots. It does this by maintaining two fields, cached_removed_snaps - the
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current removed snap set and newly_removed_snaps - newly removed snaps in the
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last epoch. In OSD::load_pgs the osd map is recovered from the pg's file store
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and passed down to OSD::_get_pool where a PGPool object is initialised with the
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map.
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With each new map we receive we call PGPool::update with the new map. In that
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function we build a list of newly removed snaps
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(pg_pool_t::build_removed_snaps) and merge that with our cached_removed_snaps.
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This function included checks to make sure we only do this update when things
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have changed or there has been a map gap.
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When we activate the pg we initialise the snap trim queue from
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cached_removed_snaps and subtract the purged_snaps we have already purged
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leaving us with the list of snaps that need to be trimmed. Trimming is later
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performed asynchronously by the snap_trim_wq.
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