Apache9 commented on a change in pull request #3942: URL: https://github.com/apache/hbase/pull/3942#discussion_r768775708
########## File path: src/main/asciidoc/_chapters/store_file_tracking.adoc ########## @@ -0,0 +1,175 @@ +//// +/** + * + * 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. + */ +//// + +[[storefiletracking]] += Store File Tracking +:doctype: book +:numbered: +:toc: left +:icons: font +:experimental: + +== Overview + +This feature introduces an abstraction layer to track store files still used/needed by store +engines, allowing for plugging different approaches of identifying store +files required by the given store. + +Historically, HBase internals have relied on creating hfiles on temporary directories first, renaming +those files to the actual store directory at operation commit time. That's a simple and convenient +way to separate transient from already finalised files that are ready to serve client reads with data. +This approach works well with strong consistent file systems, but with the popularity of less consistent +file systems, mainly Object Store file systems, dependency on rename operations starts to introduce +performance penalties. Amazon S3 Object Store, in particular, has been the most affected deployment, +due to the its lack of atomic renames, requiring an additional locking layer implemented by HBOSS, +to guarantee consistency and integrity of operations. + +With *Store File Tracking*, decision on where to originally create new hfiles and how to proceed upon +commit is delegated to the specific Store File Tracking implementation. +It can be set at individual Table or Column Family configurations, as well as in processes +*hbase-site.xml* configuration file. + +NOTE: When specified in *hbase_site.xml*, this configuration is also saved into tables configuration +at table creation time. This is to avoid dangerous configuration mismatches between processes, which +could potentially lead to data loss. + +== Available Implementations + +Store File Tracking initial version provides three builtin implementations: + +* DEFAULT +* FILE +* MIGRATION + +### DEFAULT + +As per the name, this is the Store File Tracking implementation used by default when now explicit +configuration has been defined. The DEFAULT tracker implements the standard approach using temporary +directories and renames. + +### FILE + +A file tracker implementation that creates new files straight in the store directory, avoiding the +need for rename operations. It keeps a list of committed hfiles in memory, backed by meta files, in +each store directory. Whenever a new hfile is committed, the list of _tracked files_ in the given +store is updated and a new meta file is written with this list contents, discarding the previous +meta file now containing an out dated list. + +### MIGRATION + +A special implementation to be used when swapping between Store File Tracking implementations on +pre-existing tables that already contain data, and therefore, files being tracked under an specific +logic. + +== Usage + +For fresh deployments that don't yet contain any user data, *FILE* implementation can be just set as +value for *hbase.store.file-tracker.impl* property in global *hbase-site.xml* configuration, prior +to the first hbase start. Omitting this property sets the *DEFAULT* implementation. + +### Switching implementations globally Review comment: Have you tried this operation? I do not think it works in this way... The global config will only effect new tables. So I think here you need to alter the tables one by one... -- 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: issues-unsubscr...@hbase.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
