PostgreSQL源码分析——pg_archivecleanup

pg_archivecleanup用于清理PostgreSQL WAL归档文件。指定归档目录，指定一个最老的日志段文件（在此之前的WAL日志都删掉），用法如下：

shell 复制代码

postgres@slpc:~$ pg_archivecleanup --help
pg_archivecleanup removes older WAL files from PostgreSQL archives.

Usage:
  pg_archivecleanup [OPTION]... ARCHIVELOCATION OLDESTKEPTWALFILE

Options:
  -d             generate debug output (verbose mode)
  -n             dry run, show the names of the files that would be removed
  -V, --version  output version information, then exit
  -x EXT         clean up files if they have this extension
  -?, --help     show this help, then exit

For use as archive_cleanup_command in postgresql.conf:
  archive_cleanup_command = 'pg_archivecleanup [OPTION]... ARCHIVELOCATION %r'
e.g.
  archive_cleanup_command = 'pg_archivecleanup /mnt/server/archiverdir %r'

Or for use as a standalone archive cleaner:
e.g.
  pg_archivecleanup /mnt/server/archiverdir 000000010000000000000010.00000020.backup

可参考文档：http://www.postgres.cn/docs/14/pgarchivecleanup.html

源码分析

源码不多，在pg_archivecleanup.c中。

c 复制代码

main(int argc, char **argv)
--> Initialize();	// 检查归档目录是否有效
--> SetWALFileNameForCleanup();		// 检查the oldest file we want to remain in archive是否有效
--> CleanupPriorWALFiles();  // 具体的清理归档日志

清理的代码实现如下：

c 复制代码

static void CleanupPriorWALFiles(void)
{
	int			rc;
	DIR		   *xldir;
	struct dirent *xlde;
	char		walfile[MAXPGPATH];

	if ((xldir = opendir(archiveLocation)) != NULL)
	{
		while (errno = 0, (xlde = readdir(xldir)) != NULL)
		{
			strlcpy(walfile, xlde->d_name, MAXPGPATH);
			TrimExtension(walfile, additional_ext);

			// 比较的时候，忽略时间线，
			/*
			 * We ignore the timeline part of the XLOG segment identifiers in
			 * deciding whether a segment is still needed.  This ensures that
			 * we won't prematurely remove a segment from a parent timeline.
			 * We could probably be a little more proactive about removing
			 * segments of non-parent timelines, but that would be a whole lot
			 * more complicated.
			 *
			 * We use the alphanumeric sorting property of the filenames to
			 * decide which ones are earlier than the exclusiveCleanupFileName
			 * file. Note that this means files are not removed in the order
			 * they were originally written, in case this worries you.
			 */
			if ((IsXLogFileName(walfile) || IsPartialXLogFileName(walfile)) &&
				strcmp(walfile + 8, exclusiveCleanupFileName + 8) < 0)
			{
				char		WALFilePath[MAXPGPATH * 2]; /* the file path
														 * including archive */

				/*
				 * Use the original file name again now, including any
				 * extension that might have been chopped off before testing
				 * the sequence.
				 */
				snprintf(WALFilePath, sizeof(WALFilePath), "%s/%s",
						 archiveLocation, xlde->d_name);

				if (dryrun)
				{
					/*
					 * Prints the name of the file to be removed and skips the
					 * actual removal.  The regular printout is so that the
					 * user can pipe the output into some other program.
					 */
					printf("%s\n", WALFilePath);
					pg_log_debug("file \"%s\" would be removed", WALFilePath);
					continue;
				}

				pg_log_debug("removing file \"%s\"", WALFilePath);

				rc = unlink(WALFilePath);
				if (rc != 0)
					pg_fatal("could not remove file \"%s\": %m",
							 WALFilePath);
			}
		}

		if (errno)
			pg_fatal("could not read archive location \"%s\": %m",
					 archiveLocation);
		if (closedir(xldir))
			pg_fatal("could not close archive location \"%s\": %m",
					 archiveLocation);
	}
	else
		pg_fatal("could not open archive location \"%s\": %m",
				 archiveLocation);
}