On Thu, Jul 7, 2022 at 10:14 PM Fujii Masao <masao.fu...@oss.nttdata.com> wrote: > > Hi, > > Since an exclusive backup method was dropped in v15, in v15 or later, we need > to create backup_label and tablespace_map files from the result of > pg_backup_stop() when taking a base backup using low level backup API. One > issue when doing this is that; there is no simple way to create those files > from two columns "labelfile" and "spcmapfile" that pg_backup_stop() returns > if we execute it via psql. Probaby we need to store those columns in a > temporary file and run some OS commands or script to separate that file into > backup_label and tablespace_map. This is not simple way, and which would > prevent users from migrating their backup scripts using psql from an > exclusive backup method to non-exclusive one, I'm afraid. > > To enable us to do that more easily, how about adding the pg_backup_label() > function that returns backup_label and tablespace_map? I'm thinking to make > this function available just after pg_backup_start() finishes, also even > after pg_backup_stop() finishes. For example, this function allows us to take > a backup using the following psql script file. > > ------------------------------ > SELECT * FROM pg_backup_start('test'); > \! cp -a $PGDATA /backup > SELECT * FROM pg_backup_stop(); > > \pset tuples_only on > \pset format unaligned > > \o /backup/data/backup_label > SELECT labelfile FROM pg_backup_label(); > > \o /backup/data/tablespace_map > SELECT spcmapfile FROM pg_backup_label(); > ------------------------------ > > Attached is the WIP patch to add pg_backup_label function. No tests nor docs > have been added yet, but if we can successfully reach the consensus for > adding the function, I will update the patch. > > Thought?
+1 for making it easy for the user to create backup_label and tablespace_map files. With the patch, the label_file and tblspc_map_file contents are preserved until the lifecycle of the session or the next run of pg_backup_start, I'm not sure if we need to worry more about it. Why can't we have functions like pg_create_backup_label() and pg_create_tablespace_map() which create the 'backup_label' and 'tablespace_map' files respectively in the data directory and also return the contents as output columns? Also, we can let users run these create functions only once (perhaps after the pg_backup_stop is called which is when the contents will be consistent). If we allow these functions to read the label_file or tblspc_map_file contents during the backup before stop backup, they may not be consistent. We can have a new sessionBackupState something like SESSION_BACKUP_READY_TO_COLLECT_INFO or SESSION_BACKUP_DONE and after the new function calls sessionBackupState goes to SESSION_BACKUP_NONE) and the contents of label_file and tblspc_map_file are freed up. In the docs, it's good if we can clearly specify the steps to use all of these functions. Regards, Bharath Rupireddy.