Aloys - Thank you! Will take a look and provide my feedback. - Sijie
On Tue, Nov 10, 2020 at 2:36 AM Aloys Zhang <lofterzh...@gmail.com> wrote: > Sijie, > > Sorry for the mistake, already update google doc content. > > Sijie Guo <guosi...@gmail.com> 于2020年11月10日周二 下午5:25写道： > > > Aloys, > > > > It seems that you are attaching the wrong google doc for this PIP. Isn't > > it? > > > > - Sijie > > > > On Sun, Nov 8, 2020 at 11:25 PM Aloys Zhang <lofterzh...@gmail.com> > wrote: > > > > > Hi all, > > > > > > We have drafted a proposal for supporting lightweight raw Message > > metadata > > > which can be found at > > > > > > > > > https://github.com/apache/pulsar/wiki/PIP-70%3A-Introduce-lightweight-raw-Message-metadata > > > and > > > > > > > > > https://docs.google.com/document/d/1IgnF9AJzL6JG6G4EL_xcoQxvOpd7bUXcgxFApBiPOFY > > > > > > Also， I copy it to the email thread for easier viewing. > > > > > > Any suggestions or ideas are welcomed to join the discussion. > > > > > > > > > > > > ## PIP-70： Introduce lightweight raw Message metadata > > > > > > ### 1. Motivation > > > > > > For messages in Pulsar, If we want to add new property, we always > change > > > the `MessageMetadata` in protocol(PulsarApi.proto), this kind of > property > > > could be understood by both the broker side and client side by > > > deserializing the `MessageMetadata` . But in some different cases,, the > > > property needs to be added from the broker side, Or need to be > understood > > > by the broker side in a low cost way. When the broker side gets the > > message > > > produced from the client, we could add the property at a new area, > which > > > does not combine with `MessageMetadata`, and no need deserializing > > original > > > `MessageMetadata` when gets it out ; and when the broker sends the > > message > > > to client, we could choose to filter out this part of property(or not > as > > > the client needs). We call this kind of property “raw Message > metadata”. > > By > > > this way, the “raw Message metadata” consumption is independent, and > not > > > related with the original `MessageMetadata`. > > > > > > The benefit for this kind of “raw Message metadata” is that the broker > > does > > > not need to serialize/deserialize for the protobuf-ed > `MessageMetadata`, > > > this will provide a better performance. And also could provide a lot of > > > features that are not supported yet. > > > > > > Here are some of the use cases for raw Message metadata: > > > 1) Provide ordered messages by time(broker side) sequence to make > message > > > seek by time more accurate. > > > Currently, each message has a `publish_time`, it uses client side time, > > but > > > for different producers in different clients, the time may not align > > > between clients, and cause the message order and the message time > > > (`publish_time`) order may be different. But each topic-partition only > > has > > > one owner broker, if we append broker side time in the “raw Message > > > metadata”, we could make sure the message order is aligned with broker > > side > > > time. With this feature, we could handle the message seek by time more > > > accurately. > > > > > > 2) Provide continuous message sequence-Id for messages in one > > > topic-partition. > > > MessageId is a combination of ledgerId+entryId+batchIndex; for a > > partition > > > that contains more than one ledger, the Ids inside is not continuous. > By > > > this solution, we could append a sequence-Id at the end of each > Message. > > > This will make the message sequence management earlier. > > > > > > In this proposal, we will take count in the first feature “provide > > ordered > > > message by time(broker side) sequence” mentioned above, this will be > > easier > > > to go through the proposal. > > > > > > ### 2. Message and “raw Message metadata” structure changes. > > > > > > As mentioned above, there are 2 main benefits in this proposal: > > > > > > 1. Most of all the change happened on the Broker side. > > > 2. Avoid to serialize/deserialize for the protobuf-ed > `MessageMetadata`. > > > > > > #### 2.1 Raw Message metadata structure in Protobuf > > > > > > Protobuf used a lot in Pulsar, we could use Protobuf to do the raw > > Message > > > metadata serialize/deserialize. > > > In this example, we will save the broker side timestamp when each > message > > > is sent from the broker to BookKeeper. So the definition is very > simple. > > > > > > ```protobuf > > > message RawMessageMetadata { > > > optional uint64 broker_timestamp = 1; > > > } > > > ``` > > > > > > #### 2.2 Message and “raw Message metadata” structure details > > > > > > Each message is send from producer client to broker in this frame > format: > > > > > > ``` > > > [TOTAL_SIZE] [CMD_SIZE][CMD] [MAGIC_NUMBER] [CHECKSUM] [METADATA_SIZE] > > > [METADATA] [PAYLOAD] > > > ``` > > > > > > The first 3 fields “[TOTAL_SIZE] [CMD_SIZE ] [CMD]” will be read in > > > `LengthFieldBasedFrameDecoder` and `PulsarDecoder`, and left the rest > > part > > > handled in method > > > `org.apache.pulsar.broker.service.Producer.publishMessage`. The left > part > > > “[MAGIC_NUMBER] [CHECKSUM] [METADATA_SIZE] [METADATA] [PAYLOAD]” is > > usually > > > treated as “headersAndPayload” in the code. As described above, we do > not > > > want this part to be changed at all, so we could take this part as a > > whole > > > package. > > > > > > ``` > > > [MAGIC_NUMBER] [CHECKSUM] [METADATA_SIZE] [METADATA] [PAYLOAD] ==> > > > [HEADERS_AND_PAYLOAD] > > > ``` > > > > > > We need to add some fields to make ”Raw Message metadata” work well. > > > > > > ``` > > > [RAW_METADATA_MAGIC_NUMBER] [RAW_METADATA_SIZE] [RAW_METADATA] > > > [HEADERS_AND_PAYLOAD] > > > ``` > > > > > > RAW_METADATA_MAGIC_NUMBER is used to identify whether this feature is > on, > > > and the message is handled by this feature. > > > > > > RAW_METADATA_SIZE is added for this feature, and records the size of > the > > > serialised raw Message metadata content. > > > > > > RAW_METADATA is the serialised raw Message metadata content. > > > > > > “HEADERS_AND_PAYLOAD” is the original ByteBuf data that contains > metadata > > > and payload. > > > > > > We put the new added fields before instead of after > "HEADERS_AND_PAYLOAD" > > > here, this is because > > > > > > - Firstly , the “raw Message metadata” is an addition for origin > protocol > > > and it can support this new feature without much modification for > origin > > > wire protocol, especially it does not need to serialize/deserialize for > > the > > > protobuf-ed `MessageMetadata` build from producer. > > > - Secondly, if we put new fields after "HEADERS_AND_PAYLOAD" , we can't > > > know where the offset for new added fields since we don't know the the > > > length of "PAYLOAD", and also, fields after "PAYLOAD" will change the > > CRC32 > > > checksum which means we need to recalculate the checksum one more time. > > > > > > #### 2.3 Message and “raw Message metadata” lifecycle > > > > > > The message process logic would be like this: > > > > > > 1. Producer client send the original message to broker, and parsed by > > > “PulsarDecoder”, only “[HEADERS_AND_PAYLOAD]” left; > > > 2. originally, “[HEADERS_AND_PAYLOAD]” will be write into BookKeeper by > > > method `asyncAddEntry` in `ManagedLedger`; but now we first add above > > > “[RAW_METADATA]” and related parts along with “[HEADERS_AND_PAYLOAD]”, > > then > > > write the whole ByteBuf into BookKeeper by `asyncAddEntry` ; so the > "raw > > > Message metadata" is kept together with original message in BookKeeper. > > > 3. When some features need to use this “raw Message metadata”, read the > > new > > > BookKeeper “Entry”, and get the raw Message metadata information to > > serve > > > the new feature. > > > 4. In this “provide ordered message by time(broker side) sequence” > > feature, > > > when a seek-by-time operation passes into the broker, we readout > > > “broker_timestamp” from “[RAW_METADATA]”. > > > 5. After brokers read BookKeeper Entry out, and before send to the > > consumer > > > client, we need to filter out the raw Message metadata related part, > and > > > only return “[HEADERS_AND_PAYLOAD]” part. > > > > > > By this way, we don't need to serialize/deserialize for the > protobuf-ed > > > `MessageMetadata`. > > > > > > For more details, in these steps: > > > > > > ##### a)) produced message handle and store > > > > > > Producer client side message send to broker will be handled by method > > > > > > ``` > > > publishMessageToTopic(ByteBuf headersAndPayload, long sequenceId, long > > > batchSize, boolean isChunked) > > > ``` > > > > > > in class `org.apache.pulsar.broker.service.Producer`. And it will > finally > > > call into the method `asyncAddEntry` of `ManagedLedger`, it will write > > the > > > passed in serialized message as an Entry stored in BookKeeper. > > > > > > ``` > > > void asyncAddEntry(ByteBuf headersAndPayload, AddEntryCallback > callback, > > > Object ctx) > > > ``` > > > > > > For raw Message metadata content, we need to put the current broker > > > timestamp in `message RawMessageMetadata` and use protobuf to serialize > > it > > > into `ByteBuf`. Then we put the size and content of serialized > `ByteBuf` > > > along with original `ByteBuf headersAndPayload`. > > > > > > Then “[HEADERS_AND_PAYLOAD]” turned into “[RAW_METADATA_MAGIC_NUMBER] > > > [RAW_METADATA_SIZE] [RAW_METADATA] [HEADERS_AND_PAYLOAD]” and stored in > > > BookKeeper. > > > > > > ##### b)) seek by time happens > > > > > > Originally, when a seek_by_time comes in, it will finally calls into > > class > > > > > > > > > `org.apache.pulsar.broker.service.persistent.PersistentMessageFinder.findMessages` > > > and the original logic is like this > > > > > > ```java > > > public void findMessages(final long timestamp, > > > AsyncCallbacks.FindEntryCallback callback) { > > > … > > > > > > > > > > > > cursor.asyncFindNewestMatching(ManagedCursor.FindPositionConstraint.SearchAllAvailableEntries, > > > entry -> { > > > MessageImpl msg = null; > > > msg = MessageImpl.deserialize(entry.getDataBuffer()); < > === > > > deserialize > > > return msg.getPublishTime() < timestamp; > > > }, this, callback); > > > … > > > ``` > > > > > > Find message through the topic-partition, and read out the target Entry > > > from BookKeeper, deserialize Entry into a MessageImpl and read the > > message > > > publish time that match the requirements; if not match, iterate to > > another > > > round of read another message. > > > > > > By the new design, after reading out the target Entry from BookKeeper, > it > > > does not need to do the deserialize, but only need to read out the > > > “broker_timestamp” from the “raw Message metadata”. > > > As mentioned above, the frame stored in BookKeeper is as : > > > “[RAW_METADATA_MAGIC_NUMBER] [RAW_METADATA_SIZE] [RAW_METADATA] > > > [HEADERS_AND_PAYLOAD]”, > > > > > > 1. Still use `entry.getDataBuffer()` to get the ByteBuf out; > > > 2. Read and check “[RAW_METADATA_MAGIC_NUMBER]” to see if “raw Message > > > metadata”feature is enabled; if not enabled, turn into old behaviour; > > > 3. If enabled, read “ [RAW_METADATA_SIZE] “, then read “[RAW_METADATA] > ”. > > > 4. Use protobuf to deserialize “[RAW_METADATA]”, and read > > > “broker_timestamp” out. > > > > > > ##### c)) read an entry from BookKeeper and send it to the consumer > > client > > > > > > The main logic happened in method `sendMessages` in class > > > `org.apache.pulsar.broker.service.Consumer`, the change is similar to > > above > > > “seek by time”, after read BookKeeper Entry, we need to filter out > > > "RAW_METADATA" related part, and only return “[HEADERS_AND_PAYLOAD]” > to > > > consumer client. > > > > > > ### 3 Summary of changes that need > > > > > > Here is a summary of above changes that related: > > > > > > 1. Add raw Message metadata protobuf > > > > > > ```protobuf > > > message RawMessageMetadata { > > > optional uint64 broker_timestamp = 1; > > > } > > > ``` > > > > > > 2. change how produced message is saved in bookkeeper: > > > `org.apache.pulsar.broker.service.Producer` > > > > > > 3. change how message is seek-by-time: > > > > > > > > > > > > `org.apache.pulsar.broker.service.persistent.PersistentMessageFinder.findMessages` > > > > > > 4. change how message send back to Consumer > > > `org.apache.pulsar.broker.service.Consumer` > > > > > > other changes: > > > > > > 1. A broker config to enable this raw Message metadata feature. e.g. > > > “useBrokerTimestampsForMessageSeek”. > > > 2. besides change > > > > > > > > > `org.apache.pulsar.broker.service.persistent.PersistentMessageFinder.findMessages`, > > > search other places, > > > which called `MessageImpl.deserialize(entry.getDataBuffer())` and > > > `msg.getPublishTime()`, such as > > `PersistentTopic.isOldestMessageExpired()` > > > to read message publish-time from new “raw Message metadata” instead of > > > deserialize the whole BookKeeper Entry into Message and call > > > `Message.getPublishTime()` if this feature enabled. > > > > > > > > > ### 4. Compatibility, Deprecation and Migration Plan > > > > > > For the first feature, since most of the changes are internally changes > > in > > > brokers, and it is a new feature which doesn’t change pulsar’s wire > > > protocol(between broker and client), and not changed public api. There > is > > > no backward compatibility issue. It is a newly added feature. So there > is > > > nothing to deprecate or migrate. > > > > > > In the future, we will consider the compatibility when implementing the > > > secondary feature of “continuous message sequence-Id” since we should > > send > > > messages with “sequence_id” to consumers. In this case, we will take > > > different actions dependent on the data format, feature enable or not > and > > > consumer client version . Data is new format if it contains > > > "[RAW_METADATA_MAGIC_NUMBER][RAW_METADATA_SIZE][RAW_METADATA]" and > > consumer > > > is a new version if it can process message contains "[RAW_METADATA]". > > > > > > ### 5. Test Plan > > > > > > * Unit tests for each individual change: broker/client worked well for > > > produce/consume. > > > * Integration tests or UT for end-to-end pipeline: multi producers set > > > message's time in random time order; seek-by-time could seek to the > right > > > message. > > > * Load testing for ensuring performance: seek should be more quick. > > > > > > > > > -- > > > Best, > > > Aloys. > > > > > > > > -- > Best, > Aloys. >
