org.apache.kafka.streams.kstream.SessionWindows Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
package org.apache.kafka.streams.kstream;
import org.apache.kafka.streams.internals.ApiUtils;
import org.apache.kafka.streams.processor.TimestampExtractor;
import org.apache.kafka.streams.state.SessionBytesStoreSupplier;
import java.time.Duration;
import java.util.Objects;
import static org.apache.kafka.streams.internals.ApiUtils.prepareMillisCheckFailMsgPrefix;
import static org.apache.kafka.streams.kstream.internals.WindowingDefaults.DEFAULT_RETENTION_MS;
/**
* A session based window specification used for aggregating events into sessions.
*
* Sessions represent a period of activity separated by a defined gap of inactivity.
* Any events processed that fall within the inactivity gap of any existing sessions are merged into the existing sessions.
* If the event falls outside of the session gap then a new session will be created.
*
* For example, if we have a session gap of 5 and the following data arrives:
*
* +--------------------------------------+
* | key | value | time |
* +-----------+-------------+------------+
* | A | 1 | 10 |
* +-----------+-------------+------------+
* | A | 2 | 12 |
* +-----------+-------------+------------+
* | A | 3 | 20 |
* +-----------+-------------+------------+
*
* We'd have 2 sessions for key A.
* One starting from time 10 and ending at time 12 and another starting and ending at time 20.
* The length of the session is driven by the timestamps of the data within the session.
* Thus, session windows are no fixed-size windows (c.f. {@link TimeWindows} and {@link JoinWindows}).
*
* If we then received another record:
*
* +--------------------------------------+
* | key | value | time |
* +-----------+-------------+------------+
* | A | 4 | 16 |
* +-----------+-------------+------------+
*
* The previous 2 sessions would be merged into a single session with start time 10 and end time 20.
* The aggregate value for this session would be the result of aggregating all 4 values.
*
* For time semantics, see {@link TimestampExtractor}.
*
* @see TimeWindows
* @see UnlimitedWindows
* @see JoinWindows
* @see KGroupedStream#windowedBy(SessionWindows)
* @see TimestampExtractor
*/
public final class SessionWindows {
private final long gapMs;
private final long maintainDurationMs;
private final long graceMs;
private SessionWindows(final long gapMs, final long maintainDurationMs, final long graceMs) {
this.gapMs = gapMs;
this.maintainDurationMs = maintainDurationMs;
this.graceMs = graceMs;
}
/**
* Create a new window specification with the specified inactivity gap in milliseconds.
*
* @param inactivityGapMs the gap of inactivity between sessions in milliseconds
* @return a new window specification with default maintain duration of 1 day
*
* @throws IllegalArgumentException if {@code inactivityGapMs} is zero or negative
* @deprecated Use {@link #with(Duration)} instead.
*/
@Deprecated
public static SessionWindows with(final long inactivityGapMs) {
if (inactivityGapMs <= 0) {
throw new IllegalArgumentException("Gap time (inactivityGapMs) cannot be zero or negative.");
}
return new SessionWindows(inactivityGapMs, DEFAULT_RETENTION_MS, -1);
}
/**
* Create a new window specification with the specified inactivity gap.
*
* @param inactivityGap the gap of inactivity between sessions
* @return a new window specification with default maintain duration of 1 day
*
* @throws IllegalArgumentException if {@code inactivityGap} is zero or negative or can't be represented as {@code long milliseconds}
*/
public static SessionWindows with(final Duration inactivityGap) {
final String msgPrefix = prepareMillisCheckFailMsgPrefix(inactivityGap, "inactivityGap");
return with(ApiUtils.validateMillisecondDuration(inactivityGap, msgPrefix));
}
/**
* Set the window maintain duration (retention time) in milliseconds.
* This retention time is a guaranteed lower bound for how long a window will be maintained.
*
* @return itself
* @throws IllegalArgumentException if {@code durationMs} is smaller than window gap
*
* @deprecated since 2.1. Use {@link Materialized#retention}
* or directly configure the retention in a store supplier and use
* {@link Materialized#as(SessionBytesStoreSupplier)}.
*/
@Deprecated
public SessionWindows until(final long durationMs) throws IllegalArgumentException {
if (durationMs < gapMs) {
throw new IllegalArgumentException("Window retention time (durationMs) cannot be smaller than window gap.");
}
return new SessionWindows(gapMs, durationMs, graceMs);
}
/**
* Reject out-of-order events that arrive more than {@code afterWindowEnd}
* after the end of its window.
*
* Note that new events may change the boundaries of session windows, so aggressive
* close times can lead to surprising results in which an out-of-order event is rejected and then
* a subsequent event moves the window boundary forward.
*
* @param afterWindowEnd The grace period to admit out-of-order events to a window.
* @return this updated builder
* @throws IllegalArgumentException if the {@code afterWindowEnd} is negative of can't be represented as {@code long milliseconds}
*/
public SessionWindows grace(final Duration afterWindowEnd) throws IllegalArgumentException {
final String msgPrefix = prepareMillisCheckFailMsgPrefix(afterWindowEnd, "afterWindowEnd");
final long afterWindowEndMs = ApiUtils.validateMillisecondDuration(afterWindowEnd, msgPrefix);
if (afterWindowEndMs < 0) {
throw new IllegalArgumentException("Grace period must not be negative.");
}
return new SessionWindows(
gapMs,
maintainDurationMs,
afterWindowEndMs
);
}
@SuppressWarnings("deprecation") // continuing to support Windows#maintainMs/segmentInterval in fallback mode
public long gracePeriodMs() {
// NOTE: in the future, when we remove maintainMs,
// we should default the grace period to 24h to maintain the default behavior,
// or we can default to (24h - gapMs) if you want to be super accurate.
return graceMs != -1 ? graceMs : maintainMs() - inactivityGap();
}
/**
* Return the specified gap for the session windows in milliseconds.
*
* @return the inactivity gap of the specified windows
*/
public long inactivityGap() {
return gapMs;
}
/**
* Return the window maintain duration (retention time) in milliseconds.
*
* For {@code SessionWindows} the maintain duration is at least as small as the window gap.
*
* @return the window maintain duration
* @deprecated since 2.1. Use {@link Materialized#retention} instead.
*/
@Deprecated
public long maintainMs() {
return Math.max(maintainDurationMs, gapMs);
}
@Override
public boolean equals(final Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
final SessionWindows that = (SessionWindows) o;
return gapMs == that.gapMs &&
maintainDurationMs == that.maintainDurationMs &&
graceMs == that.graceMs;
}
@Override
public int hashCode() {
return Objects.hash(gapMs, maintainDurationMs, graceMs);
}
@Override
public String toString() {
return "SessionWindows{" +
"gapMs=" + gapMs +
", maintainDurationMs=" + maintainDurationMs +
", graceMs=" + graceMs +
'}';
}
}