VSL¶

Shared Memory Logging¶

OVERVIEW¶

This document describes the format and content of all the Varnish shared memory logging tags. These tags are used by the varnishlog(1), varnishtop(1), etc. logging tools supplied with Varnish.

VSL tags¶

TIMESTAMPS¶

Timestamps are inserted in the log on completing certain events during the worker thread's task handling. The timestamps has a label showing which event was completed. The reported fields show the absolute time of the event, the time spent since the start of the task and the time spent since the last timestamp was logged.

The timestamps logged automatically by Varnish are inserted after completing events that are expected to have delays (e.g. network IO or spending time on a waitinglist). Timestamps can also be inserted from VCL using the std.timestamp() method. If one is doing time consuming tasks in the VCL configuration, it's a good idea to log a timestamp after completing that task. This keeps the timing information in subsequent timestamps from including the time spent on the VCL event.

Request handling timestamps¶

Start: The start of request processing (first byte received or restart).
Req: Complete client request received.
ReqBody: Client request body processed (discarded, cached or passed to the backend).
Waitinglist: Came off waitinglist.
Fetch: Fetch processing finished (completely fetched or ready for streaming).
Process: Processing finished, ready to deliver the client response.
Resp: Delivery of response to the client finished.
Restart: Client request is being restarted.

Pipe handling timestamps¶

Pipe: Opened a pipe to the backend and forwarded the request.
PipeSess: The pipe session has finished.

Backend fetch timestamps¶

Start: Start of the backend fetch processing.
Bereq: Backend request sent.
Beresp: Backend response headers received.
BerespBody: Backend response body received.
Retry: Backend request is being retried.
Error: Backend request failed to vcl_backend_error.

HISTORY¶

This document was initially written by Poul-Henning Kamp, and later updated by Martin Blix Grydeland.