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feat: Huge values breakdown in cluster migration (#4144)
* feat: Huge values breakdown in cluster migration Before this PR we used `RESTORE` commands for transferring data between source and target nodes in cluster slots migration. While this _works_, it has a side effect of consuming 2x memory for huge values (i.e. if a single key's value takes 10gb, serializing it will take 20gb or even 30gb). With this PR we break down huge keys into multiple commands (`RPUSH`, `HSET`, etc), respecting the existing `--serialization_max_chunk_size` flag. Part of #4100
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| Original file line number | Diff line number | Diff line change |
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| // Copyright 2024, DragonflyDB authors. All rights reserved. | ||
| // See LICENSE for licensing terms. | ||
| // | ||
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| #include "server/journal/cmd_serializer.h" | ||
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| #include "server/container_utils.h" | ||
| #include "server/journal/serializer.h" | ||
| #include "server/rdb_save.h" | ||
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| namespace dfly { | ||
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| namespace { | ||
| using namespace std; | ||
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| class CommandAggregator { | ||
| public: | ||
| using WriteCmdCallback = std::function<void(absl::Span<const string_view>)>; | ||
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| CommandAggregator(string_view key, WriteCmdCallback cb) : key_(key), cb_(cb) { | ||
| } | ||
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| ~CommandAggregator() { | ||
| CommitPending(); | ||
| } | ||
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| enum class CommitMode { kAuto, kNoCommit }; | ||
| void AddArg(string arg, CommitMode commit_mode = CommitMode::kAuto) { | ||
| agg_bytes_ += arg.size(); | ||
| members_.push_back(std::move(arg)); | ||
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| if (commit_mode != CommitMode::kNoCommit && agg_bytes_ >= serialization_max_chunk_size) { | ||
| CommitPending(); | ||
| } | ||
| } | ||
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| private: | ||
| void CommitPending() { | ||
| if (members_.empty()) { | ||
| return; | ||
| } | ||
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| args_.clear(); | ||
| args_.reserve(members_.size() + 1); | ||
| args_.push_back(key_); | ||
| for (string_view member : members_) { | ||
| args_.push_back(member); | ||
| } | ||
| cb_(args_); | ||
| members_.clear(); | ||
| } | ||
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| string_view key_; | ||
| WriteCmdCallback cb_; | ||
| vector<string> members_; | ||
| absl::InlinedVector<string_view, 5> args_; | ||
| size_t agg_bytes_ = 0; | ||
| }; | ||
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| } // namespace | ||
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| CmdSerializer::CmdSerializer(FlushSerialized cb) : cb_(std::move(cb)) { | ||
| } | ||
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| void CmdSerializer::SerializeEntry(string_view key, const PrimeValue& pk, const PrimeValue& pv, | ||
| uint64_t expire_ms) { | ||
| // We send RESTORE commands for small objects, or objects we don't support breaking. | ||
| bool use_restore_serialization = true; | ||
| if (serialization_max_chunk_size > 0 && pv.MallocUsed() > serialization_max_chunk_size) { | ||
| switch (pv.ObjType()) { | ||
| case OBJ_SET: | ||
| SerializeSet(key, pv); | ||
| use_restore_serialization = false; | ||
| break; | ||
| case OBJ_ZSET: | ||
| SerializeZSet(key, pv); | ||
| use_restore_serialization = false; | ||
| break; | ||
| case OBJ_HASH: | ||
| SerializeHash(key, pv); | ||
| use_restore_serialization = false; | ||
| break; | ||
| case OBJ_LIST: | ||
| SerializeList(key, pv); | ||
| use_restore_serialization = false; | ||
| break; | ||
| case OBJ_STRING: | ||
| case OBJ_STREAM: | ||
| case OBJ_JSON: | ||
| case OBJ_SBF: | ||
| default: | ||
| // These types are unsupported wrt splitting huge values to multiple commands, so we send | ||
| // them as a RESTORE command. | ||
| break; | ||
| } | ||
| } | ||
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| if (use_restore_serialization) { | ||
| // RESTORE sets STICK and EXPIRE as part of the command. | ||
| SerializeRestore(key, pk, pv, expire_ms); | ||
| } else { | ||
| SerializeStickIfNeeded(key, pk); | ||
| SerializeExpireIfNeeded(key, expire_ms); | ||
| } | ||
| } | ||
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| void CmdSerializer::SerializeCommand(string_view cmd, absl::Span<const string_view> args) { | ||
| journal::Entry entry(0, // txid | ||
| journal::Op::COMMAND, // single command | ||
| 0, // db index | ||
| 1, // shard count | ||
| 0, // slot-id, but it is ignored at this level | ||
| journal::Entry::Payload(cmd, ArgSlice(args))); | ||
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| // Serialize into a string | ||
| io::StringSink cmd_sink; | ||
| JournalWriter writer{&cmd_sink}; | ||
| writer.Write(entry); | ||
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| cb_(std::move(cmd_sink).str()); | ||
| } | ||
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| void CmdSerializer::SerializeStickIfNeeded(string_view key, const PrimeValue& pk) { | ||
| if (!pk.IsSticky()) { | ||
| return; | ||
| } | ||
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| SerializeCommand("STICK", {key}); | ||
| } | ||
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| void CmdSerializer::SerializeExpireIfNeeded(string_view key, uint64_t expire_ms) { | ||
| if (expire_ms == 0) { | ||
| return; | ||
| } | ||
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| SerializeCommand("PEXIRE", {key, absl::StrCat(expire_ms)}); | ||
| } | ||
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| void CmdSerializer::SerializeSet(string_view key, const PrimeValue& pv) { | ||
| CommandAggregator aggregator( | ||
| key, [&](absl::Span<const string_view> args) { SerializeCommand("SADD", args); }); | ||
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| container_utils::IterateSet(pv, [&](container_utils::ContainerEntry ce) { | ||
| aggregator.AddArg(ce.ToString()); | ||
| return true; | ||
| }); | ||
| } | ||
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| void CmdSerializer::SerializeZSet(string_view key, const PrimeValue& pv) { | ||
| CommandAggregator aggregator( | ||
| key, [&](absl::Span<const string_view> args) { SerializeCommand("ZADD", args); }); | ||
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| container_utils::IterateSortedSet( | ||
| pv.GetRobjWrapper(), | ||
| [&](container_utils::ContainerEntry ce, double score) { | ||
| aggregator.AddArg(absl::StrCat(score), CommandAggregator::CommitMode::kNoCommit); | ||
| aggregator.AddArg(ce.ToString()); | ||
| return true; | ||
| }, | ||
| /*start=*/0, /*end=*/-1, /*reverse=*/false, /*use_score=*/true); | ||
| } | ||
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| void CmdSerializer::SerializeHash(string_view key, const PrimeValue& pv) { | ||
| CommandAggregator aggregator( | ||
| key, [&](absl::Span<const string_view> args) { SerializeCommand("HSET", args); }); | ||
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| container_utils::IterateMap( | ||
| pv, [&](container_utils::ContainerEntry k, container_utils::ContainerEntry v) { | ||
| aggregator.AddArg(k.ToString(), CommandAggregator::CommitMode::kNoCommit); | ||
| aggregator.AddArg(v.ToString()); | ||
| return true; | ||
| }); | ||
| } | ||
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| void CmdSerializer::SerializeList(string_view key, const PrimeValue& pv) { | ||
| CommandAggregator aggregator( | ||
| key, [&](absl::Span<const string_view> args) { SerializeCommand("RPUSH", args); }); | ||
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| container_utils::IterateList(pv, [&](container_utils::ContainerEntry ce) { | ||
| aggregator.AddArg(ce.ToString()); | ||
| return true; | ||
| }); | ||
| } | ||
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| void CmdSerializer::SerializeRestore(string_view key, const PrimeValue& pk, const PrimeValue& pv, | ||
| uint64_t expire_ms) { | ||
| absl::InlinedVector<string_view, 5> args; | ||
| args.push_back(key); | ||
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| string expire_str = absl::StrCat(expire_ms); | ||
| args.push_back(expire_str); | ||
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| io::StringSink value_dump_sink; | ||
| SerializerBase::DumpObject(pv, &value_dump_sink); | ||
| args.push_back(value_dump_sink.str()); | ||
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| args.push_back("ABSTTL"); // Means expire string is since epoch | ||
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| if (pk.IsSticky()) { | ||
| args.push_back("STICK"); | ||
| } | ||
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| SerializeCommand("RESTORE", args); | ||
| } | ||
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| } // namespace dfly |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,44 @@ | ||
| // Copyright 2024, DragonflyDB authors. All rights reserved. | ||
| // See LICENSE for licensing terms. | ||
| // | ||
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| #pragma once | ||
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| #include <absl/types/span.h> | ||
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| #include <string> | ||
| #include <string_view> | ||
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| #include "server/table.h" | ||
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| namespace dfly { | ||
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| // CmdSerializer serializes DB entries (key+value) into command(s) in RESP format string. | ||
| // Small entries are serialized as RESTORE commands, while bigger ones (see | ||
| // serialization_max_chunk_size) are split into multiple commands (like rpush, hset, etc). | ||
| // Expiration and stickiness are also serialized into commands. | ||
| class CmdSerializer { | ||
| public: | ||
| using FlushSerialized = std::function<void(std::string)>; | ||
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| explicit CmdSerializer(FlushSerialized cb); | ||
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| void SerializeEntry(std::string_view key, const PrimeValue& pk, const PrimeValue& pv, | ||
| uint64_t expire_ms); | ||
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| private: | ||
| void SerializeCommand(std::string_view cmd, absl::Span<const std::string_view> args); | ||
| void SerializeStickIfNeeded(std::string_view key, const PrimeValue& pk); | ||
| void SerializeExpireIfNeeded(std::string_view key, uint64_t expire_ms); | ||
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| void SerializeSet(std::string_view key, const PrimeValue& pv); | ||
| void SerializeZSet(std::string_view key, const PrimeValue& pv); | ||
| void SerializeHash(std::string_view key, const PrimeValue& pv); | ||
| void SerializeList(std::string_view key, const PrimeValue& pv); | ||
| void SerializeRestore(std::string_view key, const PrimeValue& pk, const PrimeValue& pv, | ||
| uint64_t expire_ms); | ||
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| FlushSerialized cb_; | ||
| }; | ||
|
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| } // namespace dfly |
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