作者
digoal
日期
2020-10-03
标签
PostgreSQL , wal , 归档
背景
用户可能会开启归档(archive_mode=on 或者 always), 但是又忘记配置归档命令(archive_command = 默认值或空字符串), 导致wal目录堆积.
archive_mode (enum)
When archive_mode is enabled, completed WAL segments are sent to archive storage by setting archive_command. In addition to off, to disable, there are two modes: on, and always. During normal operation, there is no difference between the two modes, but when set to always the WAL archiver is enabled also during archive recovery or standby mode. In always mode, all files restored from the archive or streamed with streaming replication will be archived (again). See Section 26.2.9 for details.
archive_mode and archive_command are separate variables so that archive_command can be changed without leaving archiving mode. This parameter can only be set at server start. archive_mode cannot be enabled when wal_level is set to minimal.
archive_command (string)
The local shell command to execute to archive a completed WAL file segment. Any %p in the string is replaced by the path name of the file to archive, and any %f is replaced by only the file name. (The path name is relative to the working directory of the server, i.e., the cluster's data directory.) Use %% to embed an actual % character in the command. It is important for the command to return a zero exit status only if it succeeds. For more information see Section 25.3.1.
This parameter can only be set in the postgresql.conf file or on the server command line. It is ignored unless archive_mode was enabled at server start. If archive_command is an empty string (the default) while archive_mode is enabled, WAL archiving is temporarily disabled, but the server continues to accumulate WAL segment files in the expectation that a command will soon be provided. Setting archive_command to a command that does nothing but return true, e.g., /bin/true (REM on Windows), effectively disables archiving, but also breaks the chain of WAL files needed for archive recovery, so it should only be used in unusual circumstances.
原因很简单, 因为If archive_command is an empty string (the default) while archive_mode is enabled, WAL archiving is temporarily disabled, but the server continues to accumulate WAL segment files in the expectation that a command will soon be provided.
等于开着归档, 但是不提供归档的命令, 每个写完的wal文件在archive_status目录中的wal.ready归档状态文件被保留, 等你配置archive_command参数的归档命令去拷贝对应的wal文件.
如果要把归档开起来, 但是等未来准备好了再实现真实的拷贝, 可以配置一条返回true的命令在archive_command里面, 那么wal就不会堆积. 例如/bin/true, /usr/bin/date.
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PostgreSQL 解决方案集合
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