Package org.gridgain.internal.dcr.metastorage

Class WatermarkPersister

java.lang.Object

org.gridgain.internal.dcr.metastorage.WatermarkPersister

public class WatermarkPersister
extends Object

Coalescing, rate-limited persister for the CQ watermark of a single (replication, table) pair.

Under heavy CQ load every batch carries a fresh watermark, and a naive "write per batch" path floods the metastorage raft group (see GG-48798). This class decouples the CQ batch rate from the metastorage write rate by:

1. holding at most one in-flight write at a time;
2. coalescing intermediate watermarks into a single latest slot — the next chained write picks up the freshest value;
3. enforcing a configurable minimum interval between writes (via intervalMillisSupplier, which is re-read on every scheduling decision so cluster-config hot updates take effect on the next write).

Watermarks are monotonic and DcrStorage.putWatermark(java.lang.String, java.lang.String, byte[]) has last-write-wins semantics, so dropping intermediate values is safe — on restart, replication resumes from a watermark at most one persisted-interval old and the source re-delivers the missing tail. flush() bypasses the interval gate to guarantee a clean shutdown loses no progress.

accept(byte[]) may be called from any thread (typically a single CQ-delivery thread). Concurrent flush() from multiple threads is safe but only the first call performs the drain — subsequent calls return an already-completed future.

Constructor Summary

Constructors

Constructor	Description
WatermarkPersister(String replicationName, String tableName, Function<byte[],CompletableFuture<Void>> writer, LongSupplier intervalMillisSupplier, ScheduledExecutorService scheduler)	Constructor.

Method Summary

Modifier and Type	Method	Description
void	accept(byte[] watermarkBytes)	Offers a new watermark for persistence.
CompletableFuture<Void>	flush()	Drains the latest observed watermark to metastorage (ignoring the interval gate) and stops accepting new updates.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

WatermarkPersister

public WatermarkPersister(String replicationName,
 String tableName,
 Function<byte[],CompletableFuture<Void>> writer,
 LongSupplier intervalMillisSupplier,
 ScheduledExecutorService scheduler)

Constructor.

Parameters:

replicationName - Replication name (for logging only).

tableName - Fully-qualified table name (for logging only).

writer - Issues the actual metastorage write (typically a wrapper around DcrStorage.putWatermark(java.lang.String, java.lang.String, byte[])).

intervalMillisSupplier - Re-read on every scheduling decision so hot updates of the cluster-wide interval take effect on the next write. Negative values are clamped to 0.

scheduler - Used to fire the next write once the interval gate expires; not shut down by this class.

Method Details

accept

public void accept(byte[] watermarkBytes)

Offers a new watermark for persistence. The call is non-blocking and may not result in an immediate write: the value is stored in latest and a write is started or scheduled subject to the interval gate and the current in-flight state.

flush

public CompletableFuture<Void> flush()

Drains the latest observed watermark to metastorage (ignoring the interval gate) and stops accepting new updates. Idempotent: subsequent calls return an already-completed future. Cancels any pending scheduled trigger and waits for any in-flight write to finish before issuing the final write.

Returns:

future completing when the final write (if any) has been acknowledged.