iilyak commented on code in PR #5558:
URL: https://github.com/apache/couchdb/pull/5558#discussion_r2155424287
##########
src/fabric/src/fabric_drop_seq.erl:
##########
@@ -0,0 +1,1016 @@
+-module(fabric_drop_seq).
+
+-include_lib("mem3/include/mem3.hrl").
+-include_lib("couch/include/couch_db.hrl").
+-include_lib("couch_mrview/include/couch_mrview.hrl").
+
+-export([go/1]).
+
+-export([
+ create_peer_checkpoint_doc_if_missing/5,
+ update_peer_checkpoint_doc/5,
+ cleanup_peer_checkpoint_docs/3,
+ peer_checkpoint_doc/4,
+ peer_id_from_sig/2
+]).
+
+%% rpc
+-export([gather_drop_seq_info_rpc/1]).
+
+-type range() :: [non_neg_integer()].
+
+-type uuid() :: binary().
+
+-type seq() :: non_neg_integer().
+
+-type uuid_map() :: #{{Range :: range(), Node :: node()} => uuid()}.
+
+-type peer_checkpoints() :: #{{range(), Node :: node()} => {Uuid :: uuid(),
Seq :: seq()}}.
+
+-type history_item() :: {
+ SourceUuid :: uuid(), SourceSeq :: seq(), TargetUuid :: uuid(), TargetSeq
:: seq()
+}.
+
+-type shard_sync_history() :: #{
+ {Range :: range(), SourceNode :: node(), TargetNode :: node()} =>
[history_item()]
+}.
+
+go(DbName) ->
+ Shards0 = mem3:shards(DbName),
+ case gather_drop_seq_info(Shards0) of
+ {error, Reason} ->
+ {error, Reason};
+ {ok, #{
+ uuid_map := UuidMap,
+ peer_checkpoints := PeerCheckpoints,
+ shard_sync_history := ShardSyncHistory
+ }} ->
+ Shards1 = fully_replicated_shards_only(Shards0, ShardSyncHistory),
+ DropSeqs = calculate_drop_seqs(
+ Shards0, UuidMap, PeerCheckpoints, ShardSyncHistory
+ ),
+ Workers = lists:filtermap(
+ fun(Shard) ->
+ #shard{range = Range, node = Node, name = ShardName} =
Shard,
+ case maps:find({Range, Node}, DropSeqs) of
+ {ok, {_UuidPrefix, 0}} ->
+ false;
+ {ok, {UuidPrefix, DropSeq}} ->
+ Ref = rexi:cast(
+ Node,
+ {fabric_rpc, set_drop_seq, [
+ ShardName, UuidPrefix, DropSeq,
[?ADMIN_CTX]
+ ]}
+ ),
+ {true, Shard#shard{ref = Ref, opts = [{drop_seq,
DropSeq}]}};
+ error ->
+ false
+ end
+ end,
+ Shards1
+ ),
+ if
+ Workers == [] ->
+ %% nothing to do
+ {ok, #{}};
+ true ->
+ RexiMon = fabric_util:create_monitors(Shards1),
+ Acc0 = {#{}, length(Workers) - 1},
+ try
+ case
+ fabric_util:recv(
+ Workers, #shard.ref, fun
handle_set_drop_seq_reply/3, Acc0
+ )
+ of
+ {ok, Results} ->
+ {ok, Results};
+ {timeout, {WorkersDict, _}} ->
+ DefunctWorkers =
fabric_util:remove_done_workers(
+ WorkersDict,
+ nil
+ ),
+ fabric_util:log_timeout(
+ DefunctWorkers,
+ "set_drop_seq"
+ ),
+ {error, timeout};
+ {error, Reason} ->
+ {error, Reason}
+ end
+ after
+ rexi_monitor:stop(RexiMon)
+ end
+ end
+ end.
+
+-spec calculate_drop_seqs([#shard{}], uuid_map(), peer_checkpoints(),
shard_sync_history()) ->
+ peer_checkpoints().
+calculate_drop_seqs(Shards, UuidMap, PeerCheckpoints0, ShardSyncHistory) ->
+ PeerCheckpoints1 = substitute_splits(Shards, UuidMap, PeerCheckpoints0),
+ PeerCheckpoints2 = crossref(PeerCheckpoints1, ShardSyncHistory),
+ ShardSyncCheckpoints = latest_shard_sync_checkpoints(ShardSyncHistory),
+ maps:merge_with(fun merge_peers/3, PeerCheckpoints2, ShardSyncCheckpoints).
+
+handle_set_drop_seq_reply(ok, Worker, {Results0, Waiting}) ->
+ DropSeq = proplists:get_value(drop_seq, Worker#shard.opts),
+ [B, E] = Worker#shard.range,
+ BHex = couch_util:to_hex(<<B:32/integer>>),
+ EHex = couch_util:to_hex(<<E:32/integer>>),
+ Range = list_to_binary([BHex, "-", EHex]),
+ Results1 = maps:merge_with(
+ fun(_Key, Val1, Val2) ->
+ maps:merge(Val1, Val2)
+ end,
+ Results0,
+ #{Range => #{Worker#shard.node => DropSeq}}
+ ),
+ if
+ Waiting == 0 ->
+ {stop, Results1};
+ true ->
+ {ok, {Results1, Waiting - 1}}
+ end;
+handle_set_drop_seq_reply(Error, _, _Acc) ->
+ {error, Error}.
+
+crossref(PeerCheckpoints0, ShardSyncHistory) ->
+ PeerCheckpoints1 = maps:fold(
+ fun({Range, Node}, {Uuid, Seq}, Acc1) ->
+ Others = maps:filter(
+ fun({R, S, _T}, _History) -> R == Range andalso S == Node end,
ShardSyncHistory
+ ),
+ if
+ Seq == 0 ->
+ %% propogate any 0 checkpoint as they would not be
+ %% matched in shard sync history.
+ maps:fold(
+ fun({R, _S, T}, _History, Acc2) ->
+ maps:merge_with(fun merge_peers/3, #{{R, T} =>
{<<>>, 0}}, Acc2)
+ end,
+ Acc1,
+ Others
+ );
+ true ->
+ maps:fold(
+ fun({R, _S, T}, History, Acc2) ->
+ case
+ lists:search(
+ fun({SU, SS, _TU, _TS}) ->
+ uuids_match([Uuid, SU]) andalso SS =<
Seq
+ end,
+ History
+ )
+ of
+ {value, {_SU, _SS, TU, TS}} ->
+ maps:merge_with(fun merge_peers/3, #{{R,
T} => {TU, TS}}, Acc2);
+ false ->
+ Acc2
+ end
+ end,
+ Acc1,
+ Others
+ )
+ end
+ end,
+ PeerCheckpoints0,
+ PeerCheckpoints0
+ ),
+
+ %% mem3 sync is not hub-spoke, each iteration of crossref will add
+ %% some crossreferences. we call it again if the map changes as new
+ %% crossreferences may be possible.
+ if
+ PeerCheckpoints0 == PeerCheckpoints1 ->
+ PeerCheckpoints1;
+ true ->
+ crossref(PeerCheckpoints1, ShardSyncHistory)
+ end.
+
+%% return only the shards that have synced to by every other replica
+fully_replicated_shards_only(Shards, ShardSyncHistory) ->
+ lists:filter(
+ fun(#shard{range = Range, node = Node}) ->
+ ExpectedPeers = [
+ S#shard.node
+ || S <- Shards, S#shard.range == Range, S#shard.node /= Node
+ ],
+ ExpectedKeys = [{Range, Peer, Node} || Peer <- ExpectedPeers],
+ lists:all(fun(Key) -> maps:is_key(Key, ShardSyncHistory) end,
ExpectedKeys)
+ end,
+ Shards
+ ).
+
+-spec gather_drop_seq_info(Shards :: [#shard{}]) ->
+ {ok, peer_checkpoints(), shard_sync_history()} | {error, term()}.
+gather_drop_seq_info([#shard{} | _] = Shards) ->
+ Workers = fabric_util:submit_jobs(
+ Shards, ?MODULE, gather_drop_seq_info_rpc, []
+ ),
+ RexiMon = fabric_util:create_monitors(Workers),
+ Acc0 = #{uuid_map => #{}, peer_checkpoints => #{}, shard_sync_history =>
#{}},
+ try
+ case
+ rexi_utils:recv(
+ Workers,
+ #shard.ref,
+ fun gather_drop_seq_info_cb/3,
+ {Acc0, length(Workers) - 1},
+ fabric_util:request_timeout(),
+ infinity
+ )
+ of
+ {ok, Result} ->
+ {ok, Result};
+ {timeout, _State} ->
+ {error, timeout};
+ {error, Reason} ->
+ {error, Reason}
+ end
+ after
+ rexi_monitor:stop(RexiMon),
+ fabric_streams:cleanup(Workers)
+ end.
+
+gather_drop_seq_info_rpc(DbName) ->
+ case couch_db:open_int(DbName, []) of
+ {ok, Db} ->
+ try
+ Uuid = couch_db:get_uuid(Db),
+ Seq = couch_db:get_committed_update_seq(Db),
+ Range = mem3:range(DbName),
+ Acc0 = {#{{Range, node()} => {Uuid, Seq}}, #{}},
+ {ok, {PeerCheckpoints, ShardSyncHistory}} =
couch_db:fold_local_docs(
+ Db, fun gather_drop_seq_info_fun/2, Acc0, []
+ ),
+ rexi:reply(
+ {ok, #{
+ uuid => Uuid,
+ seq => Seq,
+ peer_checkpoints => PeerCheckpoints,
+ shard_sync_history => ShardSyncHistory
+ }}
+ )
+ after
+ couch_db:close(Db)
+ end;
+ Else ->
+ rexi:reply(Else)
+ end.
+
+gather_drop_seq_info_fun(
+ #doc{id = <<?LOCAL_DOC_PREFIX, "peer-checkpoint-", _/binary>>} = Doc,
+ {PeerCheckpoints0, ShardSyncHistory} = Acc
+) ->
+ {Props} = Doc#doc.body,
+ case couch_util:get_value(<<"update_seq">>, Props) of
+ undefined ->
+ {ok, Acc};
+ UpdateSeq ->
+ PeerCheckpoints1 = maps:merge_with(
+ fun merge_peers/3, decode_seq(UpdateSeq), PeerCheckpoints0
+ ),
+ {ok, {PeerCheckpoints1, ShardSyncHistory}}
+ end;
+gather_drop_seq_info_fun(
+ #doc{id = <<?LOCAL_DOC_PREFIX, "shard-sync-", _/binary>>} = Doc,
+ {PeerCheckpoints, ShardSyncHistory0} = Acc
+) ->
+ {Props} = Doc#doc.body,
+ case couch_util:get_value(<<"dbname">>, Props) of
+ undefined ->
+ %% not yet upgraded with new property
+ {ok, Acc};
+ DbName ->
+ Range = mem3:range(DbName),
+ {[{_SrcNode, History}]} = couch_util:get_value(<<"history">>,
Props),
+ KeyFun = fun({Item}) ->
+ {Range,
binary_to_existing_atom(couch_util:get_value(<<"source_node">>, Item)),
+
binary_to_existing_atom(couch_util:get_value(<<"target_node">>, Item))}
+ end,
+ ValueFun = fun({Item}) ->
+ {
+ couch_util:get_value(<<"source_uuid">>, Item),
+ couch_util:get_value(<<"source_seq">>, Item),
+ couch_util:get_value(<<"target_uuid">>, Item),
+ couch_util:get_value(<<"target_seq">>, Item)
+ }
+ end,
+ ShardSyncHistory1 = maps:merge(
+ maps:groups_from_list(KeyFun, ValueFun, History),
ShardSyncHistory0
+ ),
+ {ok, {PeerCheckpoints, ShardSyncHistory1}}
+ end;
+gather_drop_seq_info_fun(#doc{}, Acc) ->
+ %% ignored
+ {ok, Acc}.
+
+gather_drop_seq_info_cb({rexi_DOWN, _, _, _}, _Worker, {Acc, Count}) ->
+ {ok, {Acc, Count - 1}};
+gather_drop_seq_info_cb({rexi_EXIT, _Reason}, _Worker, {Acc, Count}) ->
+ {ok, {Acc, Count - 1}};
+gather_drop_seq_info_cb({ok, Info}, Worker, {Acc, Count}) ->
+ MergedInfo = merge_info(Worker, Info, Acc),
+ if
+ Count == 0 ->
+ {stop, MergedInfo};
+ true ->
+ {ok, {MergedInfo, Count - 1}}
+ end;
+gather_drop_seq_info_cb(_Error, _Worker, {Acc, Count}) ->
+ {ok, {Acc, Count - 1}}.
+
+merge_info(#shard{} = Shard, Info, Acc) ->
+ #{
+ uuid_map =>
+ maps:put(
+ {Shard#shard.range, Shard#shard.node}, maps:get(uuid, Info),
maps:get(uuid_map, Acc)
+ ),
+ peer_checkpoints => maps:merge_with(
+ fun merge_peers/3,
+ maps:get(peer_checkpoints, Info),
+ maps:get(peer_checkpoints, Acc)
+ ),
+ shard_sync_history => maps:merge(
+ maps:get(shard_sync_history, Info), maps:get(shard_sync_history,
Acc)
+ )
+ }.
+
+merge_peers(_Key, {Uuid1, Val1}, {Uuid2, Val2}) when
+ is_binary(Uuid1), is_binary(Uuid2), is_integer(Val1), is_integer(Val2)
+->
+ true = uuids_match([Uuid1, Uuid2]),
+ {Uuid1, min(Val1, Val2)}.
+
+uuids_match(Uuids) when is_list(Uuids) ->
+ PrefixLen = lists:min([byte_size(Uuid) || Uuid <- Uuids]),
+ binary:longest_common_prefix(Uuids) == PrefixLen.
+
+decode_seq(OpaqueSeq) ->
+ Decoded = fabric_view_changes:decode_seq(OpaqueSeq),
+ lists:foldl(
+ fun
+ ({_Node, [S, E], {Seq, Uuid, Node}}, Acc) when
+ is_integer(S),
+ is_integer(E),
+ is_integer(Seq),
+ S >= 0,
+ E > S,
+ Seq >= 0,
+ is_binary(Uuid),
+ is_atom(Node)
+ ->
+ Acc#{{[S, E], Node} => {Uuid, Seq}};
+ (_Else, Acc) ->
+ Acc
+ end,
+ #{},
+ Decoded
+ ).
+
+latest_shard_sync_checkpoints(ShardSyncHistory) ->
+ maps:fold(
+ fun({R, SN, _TN}, History, Acc) ->
+ {SU, SS, _TU, _TS} = hd(History),
+ maps:merge_with(fun merge_peers/3, #{{R, SN} => {SU, SS}}, Acc)
+ end,
+ #{},
+ ShardSyncHistory
+ ).
+
+%% A shard may have been split since a peer saw it.
+-spec substitute_splits([#shard{}], uuid_map(), peer_checkpoints()) ->
peer_checkpoints().
+substitute_splits(Shards, UuidMap, PeerCheckpoints) ->
+ maps:fold(
+ fun({[PS, PE], Node}, {Uuid, Seq}, Acc) ->
+ ShardsInRange = [
+ S
+ || #shard{range = [SS, SE]} = S <- Shards,
+ Node == S#shard.node,
+ SS >= PS andalso SE =< PE
+ ],
+ %% lookup uuid from map if substituted
+ AsMap = maps:from_list(
+ lists:filtermap(
+ fun(#shard{} = Shard) ->
+ Key = {Shard#shard.range, Shard#shard.node},
+ if
+ [PS, PE] == Shard#shard.range ->
+ {true, {Key, {Uuid, Seq}}};
+ true ->
+ case maps:find(Key, UuidMap) of
+ {ok, SubstUuid} ->
+ {true, {Key, {SubstUuid, Seq}}};
+ error ->
+ false
+ end
+ end
+ end,
+ ShardsInRange
+ )
+ ),
+ maps:merge_with(fun merge_peers/3, AsMap, Acc)
+ end,
+ #{},
+ PeerCheckpoints
+ ).
+
+create_peer_checkpoint_doc_if_missing(
+ <<"shards/", _/binary>> = DbName, Subtype, Source, PeerId, UpdateSeq
+) when
+ is_binary(DbName), is_binary(PeerId), is_integer(UpdateSeq)
+->
+ create_peer_checkpoint_doc_if_missing(
+ DbName, Subtype, Source, PeerId, pack_seq(DbName, UpdateSeq)
+ );
+create_peer_checkpoint_doc_if_missing(
+ DbName, Subtype, Source, PeerId, UpdateSeq
+) when
+ is_binary(DbName),
+ is_binary(Subtype),
+ is_binary(Source),
+ is_binary(PeerId),
+ is_integer(UpdateSeq)
+->
+ ok;
+create_peer_checkpoint_doc_if_missing(
+ <<"shards/", _/binary>> = DbName, Subtype, Source, PeerId, UpdateSeq
+) when
+ is_binary(DbName),
+ is_binary(Subtype),
+ is_binary(Source),
+ is_binary(PeerId),
+ is_binary(UpdateSeq)
+->
+ {_, Ref} = spawn_monitor(fun() ->
+ case
+ fabric:open_doc(mem3:dbname(DbName), peer_checkpoint_id(Subtype,
PeerId), [?ADMIN_CTX])
+ of
+ {ok, _} ->
+ ok;
+ {not_found, _} ->
+ update_peer_checkpoint_doc(DbName, Subtype, Source, PeerId,
UpdateSeq);
+ {error, Reason} ->
+ throw({checkpoint_commit_failure, Reason})
+ end
+ end),
+ receive
+ {'DOWN', Ref, _, _, ok} ->
+ ok;
+ {'DOWN', Ref, _, _, Else} ->
+ Else
+ end.
+
+update_peer_checkpoint_doc(
+ <<"shards/", _/binary>> = DbName, Subtype, Source, PeerId, UpdateSeq
+) when
+ is_binary(DbName),
+ is_binary(Subtype),
+ is_binary(Source),
+ is_binary(PeerId),
+ is_integer(UpdateSeq)
+->
+ update_peer_checkpoint_doc(DbName, Subtype, Source, PeerId,
pack_seq(DbName, UpdateSeq));
+update_peer_checkpoint_doc(
+ DbName, Subtype, Source, PeerId, UpdateSeq
+) when
+ is_binary(DbName),
+ is_binary(Subtype),
+ is_binary(Source),
+ is_binary(PeerId),
+ is_integer(UpdateSeq)
+->
+ ok;
+update_peer_checkpoint_doc(
+ <<"shards/", _/binary>> = DbName, Subtype, Source, PeerId, UpdateSeq
+) when
+ is_binary(DbName),
+ is_binary(Subtype),
+ is_binary(Source),
+ is_binary(PeerId),
+ is_binary(UpdateSeq)
+->
+ {_, OpenRef} = spawn_monitor(fun() ->
+ case
+ fabric:open_doc(mem3:dbname(DbName), peer_checkpoint_id(Subtype,
PeerId), [?ADMIN_CTX])
+ of
+ {ok, ExistingDoc} ->
+ exit(ExistingDoc#doc.revs);
+ {not_found, _Reason} ->
+ exit({0, []});
+ {error, Reason} ->
+ throw({checkpoint_fetch_failure, Reason})
+ end
+ end),
+ receive
+ {'DOWN', OpenRef, _, _, Revs} ->
+ NewDoc0 = peer_checkpoint_doc(PeerId, Subtype, Source, UpdateSeq),
+ NewDoc1 = NewDoc0#doc{revs = Revs},
+ {_, UpdateRef} = spawn_monitor(fun() ->
+ case fabric:update_doc(mem3:dbname(DbName), NewDoc1,
[?ADMIN_CTX]) of
+ {ok, _} ->
+ couch_log:notice(
+ "updated peer checkpoint for db:~s, subtype:~s,
source:~s, peer_id:~s, update_seq:~s",
+ [
+ DbName, Subtype, Source, PeerId, UpdateSeq
+ ]
+ ),
+ ok;
+ {error, Reason} ->
+ throw({checkpoint_commit_failure, Reason})
+ end
+ end),
+ receive
+ {'DOWN', UpdateRef, _, _, ok} ->
+ ok;
+ {'DOWN', UpdateRef, _, _, Else} ->
+ Else
+ end;
+ {'DOWN', OpenRef, _, _, not_found} ->
+ ok;
+ {'DOWN', OpenRef, _, _, Else} ->
+ Else
+ end.
+
+peer_checkpoint_doc(PeerId, Subtype, Source, UpdateSeq) when
+ is_binary(PeerId), is_binary(Subtype), is_binary(Source),
is_binary(UpdateSeq)
+->
+ #doc{
+ id = peer_checkpoint_id(Subtype, PeerId),
+ body =
+ {[
+ {<<"type">>, <<"peer-checkpoint">>},
+ {<<"subtype">>, Subtype},
+ {<<"source">>, Source},
+ {<<"update_seq">>, UpdateSeq},
+ {<<"last_updated">>, ?l2b(couch_log_util:iso8601_timestamp())}
+ ]}
+ }.
+
+peer_checkpoint_id(Subtype, PeerId) ->
+ <<?LOCAL_DOC_PREFIX, "peer-checkpoint-", Subtype/binary, "-",
PeerId/binary>>.
+
+peer_id_from_sig(DbName, Sig) when is_binary(DbName), is_binary(Sig) ->
+ Hash = couch_util:encodeBase64Url(
+ crypto:hash(sha256, [atom_to_binary(node()), $0, DbName])
+ ),
+ <<Sig/binary, "$", Hash/binary>>.
+
+pack_seq(DbName, UpdateSeq) ->
+ PrefixLen = fabric_util:get_uuid_prefix_len(),
+ DbUuid = couch_util:with_db(DbName, fun(Db) -> couch_db:get_uuid(Db) end),
+ fabric_view_changes:pack_seqs(
+ [
+ {
+ #shard{node = node(), range = mem3:range(DbName)},
+ {UpdateSeq, binary:part(DbUuid, {0, PrefixLen}), node()}
+ }
+ ]
+ ).
+
+cleanup_peer_checkpoint_docs(DbName, SubType, KeepSigs) when
+ is_binary(DbName), is_binary(SubType), is_list(KeepSigs)
+->
+ MrArgs = #mrargs{
+ view_type = map,
+ include_docs = true,
+ start_key = <<?LOCAL_DOC_PREFIX, "peer-checkpoint-", SubType/binary,
"-">>,
Review Comment:
I know we have many places in CouchDB codebase which do something like this.
However it makes it harder to read for newcomers who are often unfamiliar with
the fact that we rely on ASCII ordering.
Would you mind adding a define or helper function (with inline) so it is
self documenting. I didn't finish reading the PR, maybe there is a better place
to define these helpers.
```erlang
% approach using define
-define LOWEST_KEY(SubType, <<?LOCAL_DOC_PREFIX, "peer-checkpoint-",
SubType/binary, "-">>).
-define HIGHEST_KEY(SubType, <<?LOCAL_DOC_PREFIX, "peer-checkpoint-",
SubType/binary, ".">>).
...
start_key = ?LOWEST_KEY(SubType),
end_key = ?HIGHEST_KEY(SubType),
```
```erlang
% approach with inline function
-compile({inline, [
start_key/1,
end_key/1
]}).
start_key(SubType) ->
<<?LOCAL_DOC_PREFIX, "peer-checkpoint-", SubType/binary, "-">>.
end_key(Partition) ->
<<?LOCAL_DOC_PREFIX, "peer-checkpoint-", SubType/binary, ".">>.
...
start_key = start_key(SubType),
end_key = end_key(SubType),
```
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