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Seek to table containing key (regaining some hope)
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lib/xks/manifest.ex
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lib/xks/manifest.ex
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alias Hobbes.XKS.{Blocks, Memtable}
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import ExUnit.Assertions, only: [assert: 1]
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@memtable_level -1
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@spec new :: t
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id = next_table_id(manifest)
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:ets.insert(manifest, {{level, fk_key, fk_version, epoch}, {lk_key, lk_version, block_index, block_checksum, id}})
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:ok
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end
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@spec seek_table(t, non_neg_integer, non_neg_integer, binary, non_neg_integer) :: {:ok, tuple} | :error
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def seek_table(manifest, epoch, level, key, version) do
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seek_key = {key, version}
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# version + 1 because prev() is exclusive and we need a table with start_key <= seek_key
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# epoch = 0 because we are trying to seek the previous key in the manifest keyspace
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# E.g. if we passed epoch=10 we could get {level, key, version + 1, 9} when we want to get {level, key, version, some_epoch}
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prev_key = {level, key, version + 1, 0}
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do_seek_table(manifest, epoch, level, seek_key, prev_key, false)
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end
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defp do_seek_table(manifest, epoch, level, seek_key, prev_key, prev_tombstone?) do
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case :ets.prev_lookup(manifest, prev_key) do
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{{^level, _k, _ver, _ep} = key, _obj} when prev_tombstone? ->
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# The previous entry we saw (which is *next* in the keyspace) was a tombstone,
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# so this entry has been deleted at `epoch`
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do_seek_table(manifest, epoch, level, seek_key, key, false)
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{{^level, _k, _ver, ep} = key, _obj} when ep > epoch ->
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# This entry is not visible at `epoch`
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do_seek_table(manifest, epoch, level, seek_key, key, false)
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{{^level, _k, _ver, _ep} = key, [{_key, :tombstone}]} ->
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# This entry is visible and is a tombstone,
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# so we set the prev_tombstone? flag to cancel out the next entry
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do_seek_table(manifest, epoch, level, seek_key, key, true)
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{{^level, sk_key, sk_ver, _ep}, [{_key, value}]} ->
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# This entry is visible and may contain `seek_key`
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{ek_key, ek_ver, lb_index, lb_checksum, _id} = value
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# This invariant is guaranteed because we are calling prev(seek_key + 1) to get here
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assert {sk_key, sk_ver} <= seek_key
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case seek_key < {ek_key, ek_ver} do
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true ->
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# If seek_key < end_key, this table contains `seek_key`
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table = {:table, lb_index, lb_checksum, {sk_key, sk_ver}, {ek_key, ek_ver}}
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{:ok, table}
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false ->
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# If seek_key >= end_key, that means there is a "hole" in the keyspace
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# and there is no table which contains `seek_key`
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:error
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end
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_ ->
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# Hit the end of the level without finding a table
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:error
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end
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end
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@spec list_overlapping_tables(t, non_neg_integer, non_neg_integer, {binary, non_neg_integer}, {binary, non_neg_integer}) :: [tuple]
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lib/xks/xks.ex
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lib/xks/xks.ex
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manifest = xks.manifest
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epoch = :atomics.get(xks.epoch_atomic, 1)
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_tables = Manifest.list_overlapping_tables(manifest, epoch, 1, {key, version}, {key, version + 1})
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Manifest.seek_table(manifest, epoch, 1, key, version)
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|> dbg()
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Manifest.list_memtables(xks.manifest, epoch)
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|> Enum.find_value(:error, fn {_id, memtable} ->