Apache HTTP Server Version 2.5

Apache > HTTP Server > Documentation > Version 2.5 > Modules

# Apache Module mod_lbmethod_bybusyness

Description: | Pending Request Counting load balancer scheduler algorithm for `mod_proxy_balancer`
Status: | Extension
Module Identifier: | lbmethod_bybusyness_module
Source File: | mod_lbmethod_bybusyness.c
Compatibility: | Split off from `mod_proxy_balancer` in 2.3

### Summary

This module does not provide any configuration directives of its own. It requires the services of `mod_proxy_balancer`, and provides the `bybusyness` load balancing method.

### Topics

- Pending Request Counting Algorithm

### Directives

This module provides no directives.

### Bugfix checklist

- httpd changelog
- Known issues
- Report a bug

### See also

- `mod_proxy`
- `mod_proxy_balancer`

## Pending Request Counting Algorithm ¶

Enabled via `lbmethod=bybusyness`, this scheduler keeps track of how many requests each worker is currently assigned at present. A new request is automatically assigned to the worker with the lowest number of active requests. This is useful in the case of workers that queue incoming requests independently of Apache, to ensure that queue length stays even and a request is always given to the worker most likely to service it the fastest and reduce latency.

In the case of multiple least-busy workers, the statistics (and weightings) used by the Request Counting method are used to break the tie. Over time, the distribution of work will come to resemble that characteristic of `byrequests` (as implemented by `mod_lbmethod_byrequests`).