ibessonov commented on a change in pull request #566: URL: https://github.com/apache/ignite-3/pull/566#discussion_r789559991
########## File path: modules/page-memory/src/main/java/org/apache/ignite/internal/pagememory/FullPageId.java ########## @@ -0,0 +1,176 @@ +/* + * 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.pagememory; + +import org.apache.ignite.internal.pagememory.util.PageIdUtils; +import org.apache.ignite.internal.util.IgniteUtils; +import org.apache.ignite.lang.IgniteStringBuilder; + +/** + * Compound object used to address a page in the global page space. + * <h3>Page ID structure</h3> + * + * <p>Generally, a full page ID consists of a group ID and page ID. A page ID consists of page index (32 bits), partition ID (16 bits) and + * flags. Higher 8 bits of page ID are unused and reserved to address entries inside data pages or page ID rotation. + * + * <p>Partition ID {@code 0xFFFF} is reserved for index pages. + * + * <p>The structure of a page ID is shown in the diagram below: + * <pre> + * +---------+-----------+------------+--------------------------+ + * | 8 bits | 8 bits | 16 bits | 32 bits | + * +---------+-----------+------------+--------------------------+ + * | OFFSET | FLAGS |PARTITION ID| PAGE INDEX | + * +---------+-----------+------------+--------------------------+ + * </pre> + * + * <p><h3>Page ID rotation</h3> + * There are scenarios when we reference one page (B) from within another page (A) by page ID. It is also + * possible that this first page (B) is concurrently reused for a different purpose. In this + * case we should have a mechanism to determine that the reference from page (A) to page (B) is no longer valid. + * This is ensured by page ID rotation - together with page's (B) ID we should write some value that is incremented + * each time a page is reused (page ID rotation). This ID should be verified after page read and a page + * should be discarded if full ID is different. + * + * <p>Effective page ID is page ID with zeroed bits used for page ID rotation. + */ +public class FullPageId { + /** Null page ID. */ + public static final FullPageId NULL_PAGE = new FullPageId(-1, -1); + + /** Page ID. */ + private final long pageId; + + /** Effective page ID. */ + private final long effectivePageId; + + /** Group ID. */ + private final int groupId; + + /** + * Constructor. + * + * @param pageId Page ID. + * @param groupId Group ID. + */ + public FullPageId(long pageId, int groupId) { + this.pageId = pageId; + this.groupId = groupId; + + effectivePageId = PageIdUtils.effectivePageId(pageId); + } + + /** + * Returns a page ID. + */ + public long pageId() { + return pageId; + } + + /** + * Returns an effective page ID. + */ + public long effectivePageId() { + return effectivePageId; + } + + /** + * Returns a group ID. + */ + public int groupId() { + return groupId; + } + + /** {@inheritDoc} */ + @Override + public boolean equals(Object o) { + if (this == o) { + return true; + } + + if (!(o instanceof FullPageId)) { + return false; + } + + FullPageId that = (FullPageId) o; + + return effectivePageId == that.effectivePageId && groupId == that.groupId; + } + + /** {@inheritDoc} */ + @Override + public int hashCode() { + return hashCode0(groupId, effectivePageId); + } + + /** + * Returns hash code of the ID. Review comment: Honestly, I'm not sure yet, this one does additional hashing for some reason. -- 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]
