geode-docs/developing/partitioned_regions/automated_rebalance.html.md.erb

---
title:  Automated Rebalancing of Partitioned Region Data
---
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**Note:** This feature is experimental and is subject to change in future releases of <%=vars.product_name_long%>.

Automated rebalance triggers a rebalance
(see [Rebalancing Partitioned Region Data](rebalancing_pr_data.html))
operation based on a
time schedule.
At the scheduled intervals, the balance of the partitioned regions
is evaluated based on configured criteria.
One criterion is a minimum threshhold for number of bytes that
would be transferred if the rebalance takes place.
The other criterion uses the ratio of the number of bytes
that would be transferred to the total number of bytes in the
regions.
If the evaluation indicates the system is out of balance,
the rebalance transfer is initiated.

To enable automated rebalance, specify the rebalance manager
in the `<initializer>` attribute within the `<cache>` configuration
of the `cache.xml` file:

``` pre
<class-name> org.apache.geode.cache.util.AutoBalancer </class-name>
```

The time schedule that triggers an evaluation and possible rebalance
uses a cron-based specification in 
the `<initializer>` attribute within the `<cache>` configuration 
of the `cache.xml` file.
This scheduling specification is required.
Specify the cron expression in the Spring format.
This example specification triggers each Saturday at 3am:

``` pre
<parameter name="schedule"> 0 0 3 ? * SAT </parameter>
```

This example specification triggers once each day at 4am:

``` pre
<parameter name="schedule"> 0 0 4 * * ?</parameter>
```

The automated rebalance specifications that specify criteria for
triggering the rebalance are optional and have reasonable default values.

One criterion is a minimum number of bytes that would be transferred
if the rebalance were to take place.
The specification is in units of bytes; here is the specification
for the default value of 100MB:

``` pre
<parameter name="minimum-size"> 104857600</parameter>
```

Another criterion represents the ratio of bytes that would be transferred
to the total number of bytes in the partitioned regions,
represented as an integer percentage.
The default is 10 percent.
This example specificies 15 percent:
 
``` pre
<parameter name="size-threshold-percent"> 15 </parameter>
```