pabloem commented on a change in pull request #15549: URL: https://github.com/apache/beam/pull/15549#discussion_r799884605
########## File path: sdks/java/io/redis/src/main/java/org/apache/beam/sdk/io/redis/RedisCursor.java ########## @@ -0,0 +1,161 @@ +/* + * 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.beam.sdk.io.redis; + +import static org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Preconditions.checkNotNull; + +import java.io.ByteArrayOutputStream; +import java.io.IOException; +import java.io.Serializable; +import java.nio.ByteBuffer; +import java.util.Objects; +import javax.annotation.Nonnull; +import org.apache.beam.sdk.coders.BigEndianLongCoder; +import org.apache.beam.sdk.io.range.ByteKey; +import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.annotations.VisibleForTesting; +import org.checkerframework.checker.nullness.qual.Nullable; + +public class RedisCursor implements Comparable<RedisCursor>, Serializable { + + private final String cursor; + private final long dbSize; + private final boolean isStart; + + public static final ByteKey ZERO_KEY = ByteKey.of(0x00); + // The zero cursor that represents the start position is represented as ByteKey.of(0x00) + public static final RedisCursor ZERO_CURSOR = RedisCursor.of("0", 8, true); + // The zero cursor that represents the start position is represented as ByteKey.EMPTY + public static final RedisCursor END_CURSOR = RedisCursor.of("0", 8, false); + + public static RedisCursor of(String cursor, long dbSize, boolean isStart) { + return new RedisCursor(cursor, dbSize, isStart); + } + + private RedisCursor(String cursor, long dbSize, boolean isStart) { + this.cursor = cursor; + this.dbSize = dbSize; + this.isStart = isStart; + } + + /** + * {@link RedisCursor} implements {@link Comparable Comparable<RedisCursor>} by transforming + * the cursors to an index of the Redis table. + */ + @Override + public int compareTo(@Nonnull RedisCursor other) { + checkNotNull(other, "other"); + if ("0".equals(cursor) && "0".equals(other.cursor)) { + if (isStart && !other.isStart()) { + return -1; + } else if (!isStart && other.isStart()) { + return 1; + } else { + return 0; + } + } + return Long.compare(Long.parseLong(cursor), Long.parseLong(other.cursor)); + } + + @Override + public boolean equals(@Nullable Object o) { + if (this == o) { + return true; + } + if (o == null || getClass() != o.getClass()) { + return false; + } + RedisCursor that = (RedisCursor) o; + return dbSize == that.dbSize && isStart == that.isStart && Objects.equals(cursor, that.cursor); + } + + @Override + public int hashCode() { + return Objects.hash(cursor, dbSize, isStart); + } + + public String getCursor() { + return cursor; + } + + public long getDbSize() { + return dbSize; + } + + public boolean isStart() { + return isStart; + } + + /* + In order to write the functions that converts to and from a Redis cursor and a ByteKey the following article and + its sources were used as reference as they explain in detail how a Redis cursor is formed and how to transform it to + a sequential value that represents the current position of the scan cursor in Redis tables. + https://engineering.q42.nl/redis-scan-cursor/ + */ + @VisibleForTesting + static ByteKey redisCursorToByteKey(RedisCursor cursor) { + if ("0".equals(cursor.getCursor())) { + if (cursor.isStart()) { + return ByteKey.of(0x00); + } else { + return ByteKey.EMPTY; + } + } + int nBits = getTablePow(cursor.getDbSize()); + long cursorLong = Long.parseLong(cursor.getCursor()); + long reversed = shiftBits(cursorLong, nBits); + BigEndianLongCoder coder = BigEndianLongCoder.of(); Review comment: maybe create this coder only once. Perhaps add a member variable INSTANCE to the class BigEndianLongCoder, so that we will only create one instance, and have better performance -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
