nickva commented on a change in pull request #1972: Introduce Shard Splitting To CouchDB URL: https://github.com/apache/couchdb/pull/1972#discussion_r270163466
########## File path: src/couch/src/couch_db_split.erl ########## @@ -0,0 +1,491 @@ +% Licensed under the Apache License, Version 2.0 (the "License"); you may not +% use this file except in compliance with the License. You may obtain a copy of +% the License at +% +% http://www.apache.org/licenses/LICENSE-2.0 +% +% Unless required by applicable law or agreed to in writing, software +% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT +% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the +% License for the specific language governing permissions and limitations under +% the License. + +-module(couch_db_split). + + +-export([ + split/3, + copy_local_docs/3, + cleanup_target/2 +]). + + +-include_lib("couch/include/couch_db.hrl"). + + +-define(DEFAULT_BUFFER_SIZE, 16777216). + + +-record(state, { + source_db, + source_uuid, + targets, + pickfun, + max_buffer_size = ?DEFAULT_BUFFER_SIZE, + hashfun +}). + +-record(target, { + db, + uuid, + buffer = [], + buffer_size = 0 +}). + +-record(racc, { + id, + source_db, + target_db, + active = 0, + external = 0, + atts = [] +}). + + +% Public API + +split(Source, #{} = Targets, PickFun) when + map_size(Targets) >= 2, is_function(PickFun, 3) -> + case couch_db:open_int(Source, [?ADMIN_CTX]) of + {ok, SourceDb} -> + Engine = get_engine(SourceDb), + Partitioned = couch_db:is_partitioned(SourceDb), + HashFun = mem3_hash:get_hash_fun(couch_db:name(SourceDb)), + try + split(SourceDb, Partitioned, Engine, Targets, PickFun, HashFun) + catch + throw:{target_create_error, DbName, Error, TargetDbs} -> + cleanup_targets(TargetDbs, Engine), + {error, {target_create_error, DbName, Error}} + after + couch_db:close(SourceDb) + end; + {not_found, _} -> + {error, missing_source} + end. + + +copy_local_docs(Source, #{} = Targets0, PickFun) when + is_binary(Source), is_function(PickFun, 3) -> + case couch_db:open_int(Source, [?ADMIN_CTX]) of + {ok, SourceDb} -> + try + Targets = maps:map(fun(_, DbName) -> + {ok, Db} = couch_db:open_int(DbName, [?ADMIN_CTX]), + #target{db = Db, uuid = couch_db:get_uuid(Db)} + end, Targets0), + SourceName = couch_db:name(SourceDb), + try + State = #state{ + source_db = SourceDb, + source_uuid = couch_db:get_uuid(SourceDb), + targets = Targets, + pickfun = PickFun, + hashfun = mem3_hash:get_hash_fun(SourceName) + }, + copy_local_docs(State), + ok + after + maps:map(fun(_, #target{db = Db} = T) -> + couch_db:close(Db), + T#target{db = undefined} + end, Targets) + end + after + couch_db:close(SourceDb) + end; + {not_found, _} -> + {error, missing_source} + end. + + +cleanup_target(Source, Target) when is_binary(Source), is_binary(Target) -> + case couch_db:open_int(Source, [?ADMIN_CTX]) of + {ok, SourceDb} -> + try + delete_target(Target, get_engine(SourceDb)) + after + couch_db:close(SourceDb) + end; + {not_found, _} -> + {error, missing_source} + end. + + +% Private Functions + +split(SourceDb, Partitioned, Engine, Targets0, PickFun, {M, F, A} = HashFun) -> + Targets = maps:fold(fun(Key, DbName, Map) -> + case couch_db:validate_dbname(DbName) of + ok -> + ok; + {error, E} -> + throw({target_create_error, DbName, E, Map}) + end, + {ok, Filepath} = couch_server:get_engine_path(DbName, Engine), + Opts = [create, ?ADMIN_CTX] ++ case Partitioned of + true -> [{props, [{partitioned, true}, {hash, [M, F, A]}]}]; + false -> [] + end, + case couch_db:start_link(Engine, DbName, Filepath, Opts) of + {ok, Db} -> + Map#{Key => #target{db = Db}}; + {error, Error} -> + throw({target_create_error, DbName, Error, Map}) + end + end, #{}, Targets0), + Seq = couch_db:get_update_seq(SourceDb), + State1 = #state{ + source_db = SourceDb, + targets = Targets, + pickfun = PickFun, + hashfun = HashFun, + max_buffer_size = get_max_buffer_size() + }, + State2 = copy_docs(State1), + State3 = copy_checkpoints(State2), + State4 = copy_meta(State3), + State5 = copy_purge_info(State4), + State6 = set_targets_update_seq(State5), + stop_targets(State6#state.targets), + {ok, Seq}. + + +cleanup_targets(#{} = Targets, Engine) -> + maps:map(fun(_, #target{db = Db} = T) -> + ok = stop_target_db(Db), + delete_target(couch_db:name(Db), Engine), + T + end, Targets). + + +stop_targets(#{} = Targets) -> + maps:map(fun(_, #target{db = Db} = T) -> + {ok, Db1} = couch_db_engine:commit_data(Db), + ok = stop_target_db(Db1), + T + end, Targets). + + +stop_target_db(Db) -> + couch_db:close(Db), + Pid = couch_db:get_pid(Db), + catch unlink(Pid), + catch exit(Pid, kill), + ok. + + +delete_target(DbName, Engine) -> + RootDir = config:get("couchdb", "database_dir", "."), + {ok, Filepath} = couch_server:get_engine_path(DbName, Engine), + DelOpt = [{context, compaction}, sync], + couch_db_engine:delete(Engine, RootDir, Filepath, DelOpt). + + +pick_target(DocId, #state{} = State, #{} = Targets) -> + #state{pickfun = PickFun, hashfun = HashFun} = State, + Key = PickFun(DocId, maps:keys(Targets), HashFun), + {Key, maps:get(Key, Targets)}. + + +set_targets_update_seq(#state{targets = Targets} = State) -> + Seq = couch_db:get_update_seq(State#state.source_db), + Targets1 = maps:map(fun(_, #target{db = Db} = Target) -> + {ok, Db1} = couch_db_engine:set_update_seq(Db, Seq), + Target#target{db = Db1} + end, Targets), + State#state{targets = Targets1}. + + +copy_checkpoints(#state{} = State) -> + #state{source_db = Db, source_uuid = SrcUUID, targets = Targets} = State, + FoldFun = fun(#doc{id = Id} = Doc, Acc) -> + UpdatedAcc = case Id of + <<?LOCAL_DOC_PREFIX, "shard-sync-", _/binary>> -> + % Transform mem3 internal replicator checkpoints to avoid + % rewinding the changes feed when it sees the new shards + maps:map(fun(_, #target{uuid = TgtUUID, buffer = Docs} = T) -> + Doc1 = update_checkpoint_doc(SrcUUID, TgtUUID, Doc), + T#target{buffer = [Doc1 | Docs]} + end, Acc); + <<?LOCAL_DOC_PREFIX, "purge-", _/binary>> -> + % Copy purge checkpoints to all shards + maps:map(fun(_, #target{buffer = Docs} = T) -> + T#target{buffer = [Doc | Docs]} + end, Acc); + <<?LOCAL_DOC_PREFIX, _/binary>> -> + % Skip copying these that will be done during + % local docs top off right before the shards are switched + Acc + end, + {ok, UpdatedAcc} + end, + {ok, Targets1} = couch_db_engine:fold_local_docs(Db, FoldFun, Targets, []), + Targets2 = maps:map(fun(_, #target{db = TDb, buffer = Docs} = T) -> + case Docs of + [] -> + T; + [_ | _] -> + Docs1 = lists:reverse(Docs), + {ok, TDb1} = couch_db_engine:write_doc_infos(TDb, [], Docs1), + {ok, TDb2} = couch_db_engine:commit_data(TDb1), + T#target{db = TDb2, buffer = []} + end + end, Targets1), + State#state{targets = Targets2}. + + +update_checkpoint_doc(Old, New, #doc{body = {Props}} = Doc) -> + NewProps = case couch_util:get_value(<<"target_uuid">>, Props) of + Old -> + replace_kv(Props, {<<"target_uuid">>, Old, New}); + Other when is_binary(Other) -> + replace_kv(Props, {<<"source_uuid">>, Old, New}) + end, + NewId = update_checkpoint_id(Doc#doc.id, Old, New), + Doc#doc{id = NewId, body = {NewProps}}. + + +update_checkpoint_id(Id, Old, New) -> + OldHash = mem3_rep:local_id_hash(Old), + NewHash = mem3_rep:local_id_hash(New), + binary:replace(Id, OldHash, NewHash). + + +replace_kv({[]}, _) -> + {[]}; +replace_kv({KVs}, Replacement) -> + {[replace_kv(KV, Replacement) || KV <- KVs]}; +replace_kv([], _) -> + []; +replace_kv(List, Replacement) when is_list(List) -> + [replace_kv(V, Replacement) || V <- List]; +replace_kv({K, V}, {K, V, NewV}) -> + {K, NewV}; +replace_kv({K, V}, Replacement) -> + {K, replace_kv(V, Replacement)}; +replace_kv(V, _) -> + V. + + +copy_meta(#state{source_db = SourceDb, targets = Targets} = State) -> + RevsLimit = couch_db:get_revs_limit(SourceDb), + {SecProps} = couch_db:get_security(SourceDb), + PurgeLimit = couch_db:get_purge_infos_limit(SourceDb), + Targets1 = maps:map(fun(_, #target{db = Db} = T) -> + {ok, Db1} = couch_db_engine:set_revs_limit(Db, RevsLimit), + {ok, Db2} = couch_db_engine:set_security(Db1, SecProps), + {ok, Db3} = couch_db_engine:set_purge_infos_limit(Db2, PurgeLimit), + T#target{db = Db3} + end, Targets), + State#state{targets = Targets1}. + + +copy_purge_info(#state{source_db = Db} = State) -> + {ok, NewState} = couch_db:fold_purge_infos(Db, 0, fun purge_cb/2, State), + Targets = maps:map(fun(_, #target{} = T) -> + commit_purge_infos(T) + end, NewState#state.targets), + NewState#state{targets = Targets}. + + +acc_and_flush(Item, #target{}= Target, MaxBuffer, FlushCb) -> + #target{buffer = Buffer, buffer_size = BSize} = Target, + BSize1 = BSize + ?term_size(Item), + Target1 = Target#target{buffer = [Item | Buffer], buffer_size = BSize1}, + case BSize1 > MaxBuffer of + true -> FlushCb(Target1); + false -> Target1 + end. + + +purge_cb({_PSeq, _UUID, Id, _Revs} = PI, #state{targets = Targets} = State) -> + {Key, Target} = pick_target(Id, State, Targets), + MaxBuffer = State#state.max_buffer_size, + Target1 = acc_and_flush(PI, Target, MaxBuffer, fun commit_purge_infos/1), + {ok, State#state{targets = Targets#{Key => Target1}}}. + + +commit_purge_infos(#target{buffer = [], db = Db} = Target) -> + Target#target{db = Db}; + +commit_purge_infos(#target{buffer = PIs0, db = Db} = Target) -> + PIs = lists:reverse(PIs0), + {ok, Db1} = couch_db_engine:copy_purge_infos(Db, PIs), + {ok, Db2} = couch_db_engine:commit_data(Db1), + Target#target{buffer = [], buffer_size = 0, db = Db2}. + + +copy_docs(#state{source_db = Db} = State) -> + {ok, NewState} = couch_db:fold_changes(Db, 0, fun changes_cb/2, State), + CommitTargets = maps:map(fun(_, #target{} = T) -> + commit_docs(T) + end, NewState#state.targets), + NewState#state{targets = CommitTargets}. + + +% Backwards compatibility clause. Seq trees used to hold #doc_infos at one time +changes_cb(#doc_info{id = Id}, #state{source_db = Db} = State) -> + [FDI = #full_doc_info{}] = couch_db_engine:open_docs(Db, [Id]), + changes_cb(FDI, State); + +changes_cb(#full_doc_info{id = Id} = FDI, #state{} = State) -> + #state{source_db = SourceDb, targets = Targets} = State, + {Key, Target} = pick_target(Id, State, Targets), + FDI1 = process_fdi(FDI, SourceDb, Target#target.db), + MaxBuffer = State#state.max_buffer_size, + Target1 = acc_and_flush(FDI1, Target, MaxBuffer, fun commit_docs/1), + {ok, State#state{targets = Targets#{Key => Target1}}}. + + +commit_docs(#target{buffer = [], db = Db} = Target) -> + Target#target{db = Db}; + +commit_docs(#target{buffer = FDIs, db = Db} = Target) -> + Pairs = [{not_found, FDI} || FDI <- lists:reverse(FDIs)], + {ok, Db1} = couch_db_engine:write_doc_infos(Db, Pairs, []), + {ok, Db2} = couch_db_engine:commit_data(Db1), + Target#target{buffer = [], buffer_size = 0, db = Db2}. + + +process_fdi(FDI, SourceDb, TargetDb) -> + #full_doc_info{id = Id, rev_tree = RTree} = FDI, + Acc = #racc{id = Id, source_db = SourceDb, target_db = TargetDb}, + {NewRTree, NewAcc} = couch_key_tree:mapfold(fun revtree_cb/4, Acc, RTree), + {Active, External} = total_sizes(NewAcc), + FDI#full_doc_info{ + rev_tree = NewRTree, + sizes = #size_info{active = Active, external = External} + }. + + +revtree_cb(_Rev, _Leaf, branch, Acc) -> + {[], Acc}; + +revtree_cb({Pos, RevId}, Leaf, leaf, Acc) -> + #racc{id = Id, source_db = SourceDb, target_db = TargetDb} = Acc, + #leaf{deleted = Deleted, ptr = Ptr} = Leaf, + Doc0 = #doc{ + id = Id, + revs = {Pos, [RevId]}, + deleted = Deleted, + body = Ptr + }, + Doc1 = couch_db_engine:read_doc_body(SourceDb, Doc0), + #doc{body = Body, atts = AttInfos0} = Doc1, + External = if not is_binary(Body) -> ?term_size(body); true -> + couch_compress:uncompressed_size(Body) + end, + AttInfos = if not is_binary(AttInfos0) -> AttInfos0; true -> + couch_compress:decompress(AttInfos0) + end, + Atts = [process_attachment(Att, SourceDb, TargetDb) || Att <- AttInfos], Review comment: Yes. If process_attachment blows the whole thing blow up. ``` 1> [throw(bam) || true]. ** exception throw: bam 2> ``` ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services
