The trace file of Http agents are constructed in a similar way as the SRM trace files. It consists of multiple entries, each of which occupies one line. The format of each entry is:
| Time | ObjectID | Object Values |
There are three types of objects: client (C), cache (E) and server (S). Following is a complete enumeration of all possible events and value types associated with these three types of objects.
| Object Type | Event Type | Values |
| E | HIT | Prefix |
| E | MISS | Prefix z RequestSize |
| E | IMS | Prefix z Size t CacheEntryTime |
| E | REF | p PageID s ServerID z Size |
| E | UPD | p PageID m LastModifiedTime z PageSize |
| s ServerID | ||
| E | GUPD | z PageSize |
| E | SINV | p PageID m LastModTime z PageSize |
| E | GINV | p PageID m LastModTime |
| E | SPF | p PageID c DestCache |
| E | RPF | p PageID c SrcCache |
| E | ENT | p PageID m LastModifiedTime z PageSize |
| s ServerID | ||
| C | GET | p PageID s PageServerID z RequestSize |
| C | STA | p PageID s OrigServerID l StaleTime |
| C | RCV | p PageID s PageServerID l ResponseTime z PageSize |
| S | INV | p PageID m LastModifiedTime z Size |
| S | UPD | p PageID m LastModifiedTime z Size |
| S | SND | p PageID m LastModifiedTime z PageSize |
| t Requesttype | ||
| S | MOD | p PageID n NextModifyTime |
Prefix is the information common to all trace entries. It includes:
| p PageID | c RequestClientID | s PageServerID |
Short Explaination of event operations:
| Object Type | Event Type | Explaination |
| E | HIT | Cache hit. PageSererID is the id of the ``owner'' of the page. |
| E | MISS | Cache miss. In this case the cache will send a request to the server to fetch the page. |
| E | IMS | If-Modified-Since. Used by TTL procotols to validate an expired page. |
| E | REF | Page refetch. Used by invalidation protocols to refetch an invalidated page. |
| E | UPD | Page update. Used by invalidation protocols to ``push'' updates |
| from parent cache to children caches. | ||
| E | SINV | Send invalidation. |
| E | GINV | Get invalidation. |
| E | SPF | Send a pro forma |
| E | RPF | Receive a pro forma |
| E | ENT | Enter a page into local page cache. |
| C | GET | Client sends a request for a page. |
| C | STA | Client gets a stale hit. OrigModTime is the modification time |
| in the web server, CurrModTime is the local page's modification time. | ||
| C | RCV | Client receives a page. |
| S | SND | Server send a response. |
| S | UPD | Server pushes a page update to its ``primary cache''. Used by invalidation protocol only. |
| S | INV | Server sends an invalidation message. Used by invalidation protocol only. |
| S | MOD | Server modified a page. The page will be modified next at NextModifyTime. |