10. Delay Pools

10.1 Introduction

A DelayPool is a Composite used to manage bandwidth for any request assigned to the pool by an access expression. DelayId's are a used to manage the bandwith on a given request, whereas a DelayPool manages the bandwidth availability and assigned DelayId's.

10.2 Extending Delay Pools

A CompositePoolNode is the base type for all members of a DelayPool. Any child must implement the RefCounting primitives, as well as five delay pool functions:

1. stats() - provide cachemanager statistics for itself.
2. dump() - generate squid.conf syntax for the current configuration of the item.
3. update() - allocate more bandwith to all buckets in the item.
4. parse() - accept squid.conf syntax for the item, and configure for use appropriately.
5. id() - return a DelayId entry for the current item.

A DelayIdComposite is the base type for all delay Id's. Concrete Delay Id's must implement the refcounting primitives, as well as two delay id functions:

1. bytesWanted() - return the largest amount of bytes that this delay id allows by policy.
2. bytesIn() - record the use of bandwidth by the request(s) that this delayId is monitoring.

Composite creation is currently under design review, so see the DelayPool class and follow the parse() code path for details.

10.3 Neat things that could be done.

With the composite structure, some neat things have become possible. For instance:

1. Dynamically defined pool arrangements - for instance an aggregate (class 1) combined with the per-class-C-net tracking of a class 3 pool, without the individual host tracking. This differs from a class 3 pool with -1/-1 in the host bucket, because no memory or cpu would be used on hosts, whereas with a class 3 pool, they are allocated and used.
2. Per request bandwidth limits - a delayId that contains it's own bucket could limit each request independently to a given policy, with no aggregate restrictions.