Avoiding too many open files in a fast fail way

[Fungo Wang]

For bug https://bugs.launchpad.net/percona-xtrabackup/+bug/1183322, there is no perfect way to avoid holding ibd file handle and make sure backup is valid. So each ibd file's handle is hold before being backed up, and this can cause Too many open files in system(23) error if there are too many ibd.

This issue is amplified in cloud or multi tenant environment for which there may be many mysqld instances in one host.

There is a `--close-files` option which will not keep files opened if specified, but this can lead to corrupt backup.

As Alexey described in bug#1183322
> 1. it can detect a renamed tablespace if at the time it has to open it for copying the space ID from first page (or inode from the filesystem, it doesn't matter) doesn't match space ID or inode this tablespace had at the time when the list of files was created. So detecting such conditions is the easy part.

Detecting ibd space id mismatch can be easily implemented.

I think PXB can add such detecting logic and failed if space id mismatch encountered. For cloud environment backup failure is OK, just try again.

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PXB-1492