Package io.debezium.connector.mysql.legacy

Class EventBuffer

java.lang.Object
io.debezium.connector.mysql.legacy.EventBuffer
class EventBuffer extends Object
This class represents a look-ahead buffer that allows Debezium to accumulate binlog events and decide if the last event in transaction is either ROLLBACK or COMMIT. The incoming events are either supposed to be in transaction or out-of-transaction. When out-of-transaction they are sent directly into the destination handler. When in transaction the event goes through the buffering.

The reason for the buffering is that the binlog contains rolled back transactions in some cases. E.g. that's the case when a temporary table is dropped (see DBZ-390). For rolled back transactions we may not propagate any of the contained events, hence the buffering is applied.

The transaction start is identified by a BEGIN event. Transaction is ended either by COMMIT event or by XID an event.

If there are more events that can fit to the buffer then:

  • Binlog position is recorded for the first event not fitting into the buffer
  • Binlog position is recorded for the commit event
  • Buffer content is sent to the final handler
  • Binlog position is rewound and all events between the above recorded positions are sent to the final handler
Author:
Jiri Pechanec

  • Field Details

    • LOGGER

      private static final org.slf4j.Logger LOGGER

    • capacity

      private final int capacity

    • buffer

      private final Queue<com.github.shyiko.mysql.binlog.event.Event> buffer

    • reader

      private final BinlogReader reader

    • txStarted

      private boolean txStarted

    • largeTxNotBufferedPosition

      private BinlogReader.BinlogPosition largeTxNotBufferedPosition
      Contains the position of the first event that has not fit into the buffer.

    • forwardTillPosition

      private BinlogReader.BinlogPosition forwardTillPosition
      Contains the position of the last event belonging to the transaction that has not fit into the buffer.

  • Constructor Details

    • EventBuffer

      public EventBuffer(int capacity, BinlogReader reader)

  • Method Details

    • add

      public void add(com.github.shyiko.mysql.binlog.event.Event event)
      An entry point to the buffer that should be used by BinlogReader to push events.
      Parameters:
      event - to be stored in the buffer

    • isReplayingEventsBeyondBufferCapacity

      private boolean isReplayingEventsBeyondBufferCapacity()
      Whether we are replaying TX events from binlog that have not fit into the buffer before

    • addToBuffer

      private void addToBuffer(com.github.shyiko.mysql.binlog.event.Event event)
      Adds an event to the buffer if there is a space available. Records binlog position for the first event that does not fit for later replay.
      Parameters:
      event -

    • switchToBufferFullMode

      private void switchToBufferFullMode()

    • isInBufferFullMode

      private boolean isInBufferFullMode()

    • consumeEvent

      private void consumeEvent(com.github.shyiko.mysql.binlog.event.Event event)

    • beginTransaction

      private void beginTransaction(com.github.shyiko.mysql.binlog.event.Event event)

    • completeTransaction

      private void completeTransaction(boolean wellFormed, com.github.shyiko.mysql.binlog.event.Event event)
      Sends all events from the buffer int a final handler. For large transactions it executes rewind of binlog reader back to the first event that was not stored in the buffer.
      Parameters:
      wellFormed -
      event -

    • rollbackTransaction

      private void rollbackTransaction()

    • clear

      private void clear()
      Cleans-up the buffer after the transaction is either thrown away or streamed into a Kafka topic