# Frequently asked questions

## Does Percona XtraBackup 8.0 support making backups of databases in versions prior to 8.0?

*Percona XtraBackup* 8.0 does not support making backups of databases
created in versions prior to 8.0 of *MySQL*, *Percona Server for MySQL* or
*Percona XtraDB Cluster*. As the changes that *MySQL* 8.0 introduced
in *data dictionaries*, *redo log* and *undo log* are incompatible
with previous versions, it is currently impossible for *Percona XtraBackup*
8.0 to also support versions prior to 8.0.

Due to changes in MySQL 8.0.20 released by Oracle at the end of April 2020,
*Percona XtraBackup* 8.0, up to version 8.0.11, is not compatible with
MySQL version 8.0.20 or
higher, or Percona products that are based on it: Percona Server for MySQL
and
Percona XtraDB Cluster.

For more information,
see [Percona XtraBackup 8.x and MySQL 8.0.20](https://www.percona.com/blog/2020/04/28/percona-xtrabackup-8-x-and-mysql-8-0-20/)

## Why will `innobackupex` not run in Percona XtraBackup 8.0?

**innobackupex** has been removed from *Percona XtraBackup*
8.0 in favor of **xtrabackup**.

## Are you aware of any web-based backup management tools (commercial or not) built around *Percona XtraBackup*?

[Zmanda Recovery Manager](http://www.zmanda.com/zrm-mysql-enterprise.html)
is a commercial tool that uses *Percona XtraBackup* for Non-Blocking Backups:

> *“ZRM provides support for non-blocking backups of MySQL using Percona
> XtraBackup. ZRM with \*Percona XtraBackup* provides resource utilization
> management by providing throttling based on the number of IO operations
> per
> second. *Percona XtraBackup* based backups also allow for table level
> recovery
> even though the backup was done at the database level (needs the recovery
> database server to be *Percona Server for MySQL* with XtraDB).”\*

## xtrabackup binary fails with a floating point exception

In most of the cases this is due to not having installed the required
libraries
(and version) by *xtrabackup*. Installing the *GCC* suite with the
supporting
libraries and recompiling *xtrabackup* solves the issue. See
[Compiling and Installing from Source Code](compile-xtrabackup.md) for instructions on the
procedure.

## How xtrabackup handles the ibdata/ib_log files on restore if they aren’t in mysql datadir?

In case the `ibdata` and `ib_log` files are located in different
directories outside the datadir, you will have to put them in their
proper
place after the logs have been applied.

## Backup fails with Error 24: ‘Too many open files’

This usually happens when database being backed up contains large amount of
files and *Percona XtraBackup* can’t open all of them to create a
successful
backup. In order to avoid this error the operating system should be
configured
appropriately so that *Percona XtraBackup* can open all its files. On
Linux,
this can be done with the `ulimit` command for specific backup session or
by
editing the `/etc/security/limits.conf` to change it globally (**NOTE**:
the maximum possible value that can be set up is `1048576` which is a
hard-coded constant in the Linux kernel).

## How to deal with skipping of redo logs for DDL operations?

To prevent creating corrupted backups when running DDL operations,
Percona XtraBackup aborts if it detects that redo logging is disabled.
In this case, the following error is printed:

```{.text .no-copy}
[FATAL] InnoDB: An optimized (without redo logging) DDL operation has been performed. All modified pages may not have been flushed to the disk yet.
Percona XtraBackup will not be able to take a consistent backup. Retry the backup operation.
```

!!! note
   
    Redo logging is disabled during
    a [sorted index build](https://dev.mysql.com/doc/refman/8.0/en/sorted-index-builds.html). To avoid this error,
    Percona XtraBackup can use metadata locks on tables while they are copied:

* To block all DDL operations, use the `--lock-ddl` option
  that issues `LOCK TABLES FOR BACKUP`.


* If `LOCK TABLES FOR BACKUP` is not supported,
  you can block DDL for each table
  before XtraBackup starts to copy it
  and until the backup is completed
  using the `--lock-ddl-per-table` option.

!!! note
   
    As of *Percona XtraBackup* 8.0.15, the –lock-ddl-per-table option
    is deprecated.
    Use the `--lock-ddl` option.