ibessonov commented on code in PR #5005: URL: https://github.com/apache/ignite-3/pull/5005#discussion_r1906990614
########## modules/raft/src/main/java/org/apache/ignite/internal/raft/storage/TermCache.java: ########## @@ -0,0 +1,127 @@ +/* + * 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.ignite.internal.raft.storage; + +import static org.apache.ignite.internal.util.IgniteUtils.isPow2; + +import org.apache.ignite.raft.jraft.entity.LogId; + +/** + * Cyclic buffer to cache several last term values for log storage. + */ +public class TermCache { + private final int mask; + private final long[] indexes; + private final long[] terms; + + // Head position. -1 means the cache is empty. + private int head = -1; + + // Tail position. Might be equal to head if the cache only has a single term. + private int tail; + + /** + * Constructor. + * + * @param capacity Cache capacity. Must be a power of 2. Should be a small value, term update is a rare operation. + */ + public TermCache(int capacity) { + assert isPow2(capacity) : "Capacity must be a power of 2"; + + this.mask = capacity - 1; + this.indexes = new long[capacity]; + this.terms = new long[capacity]; + } + + /** + * Should be called when appending a new log entry. + */ + public void append(LogId id) { + // Cache is empty. + if (head == -1) { + head = 0; + indexes[tail] = id.getIndex(); + terms[tail] = id.getTerm(); + + return; + } + + // Terms has not changed, nothing to update. + if (terms[tail] == id.getTerm()) { + return; + } + + tail = (tail + 1) & mask; + indexes[tail] = id.getIndex(); + terms[tail] = id.getTerm(); + + // Handle buffer overflow by moving head to the next position. + if (tail == head) { + head = (head + 1) & mask; + } + } + + private int findIndex(long index) { + // Could be replaced with a binary search, but why bother for such a small cache. + for (int i = tail; i != head; i = (i - 1) & mask) { + if (index >= indexes[i]) { + return i; + } + } + + return head; + } + + /** + * Lookup term for the given index. Returns {@code -1} if the index is not found in the cache. + */ + public long lookup(long idx) { + if (head == -1 || idx < indexes[head]) { + return -1; + } + + return terms[findIndex(idx)]; + } + + /** + * Resets the cache to the initial state. + */ + public void reset() { + head = -1; + tail = 0; + } + + /** + * Truncates the cache to the given index, deleting all information for indexes greater than or equal to the given one. + */ + public void truncate(long idx) { Review Comment: Yes, thank you! -- 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: notifications-unsubscr...@ignite.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
