VSL

Varnish Shared Memory Logging

Manual section:

7

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

BackendClose - Backend connection closed

Logged when a backend connection is closed.

The format is:

%d %s %s [ %s ]
|  |  |    |
|  |  |    +- Optional reason
|  |  +------ "close" or "recycle"
|  +--------- Backend display name
+------------ Connection file descriptor
BackendOpen - Backend connection opened

Logged when a new backend connection is opened.

The format is:

%d %s %s %s %s %s %s
|  |  |  |  |  |  |
|  |  |  |  |  |  +- "connect" or "reuse"
|  |  |  |  |  +---- Local port
|  |  |  |  +------- Local address
|  |  |  +---------- Remote port
|  |  +------------- Remote address
|  +---------------- Backend display name
+------------------- Connection file descriptor
Backend_health - Backend health check

The result of a backend health probe.

The format is:

%s %s %s %s %u %u %u %f %f %s
|  |  |  |  |  |  |  |  |  |
|  |  |  |  |  |  |  |  |  +- Probe HTTP response / error information
|  |  |  |  |  |  |  |  +---- Average response time
|  |  |  |  |  |  |  +------- Response time
|  |  |  |  |  |  +---------- Probe window size
|  |  |  |  |  +------------- Probe threshold level
|  |  |  |  +---------------- Number of good probes in window
|  |  |  +------------------- Probe window bits
|  |  +---------------------- "healthy" or "sick"
|  +------------------------- "Back", "Still" or "Went"
+---------------------------- Backend name

Probe window bits are:

'-': Could not connect
'4': Good IPv4
'6': Good IPv6
'U': Good UNIX
'x': Error Xmit
'X': Good Xmit
'r': Error Recv
'R': Good Recv
'H': Happy

When the backend is just created, the window bits for health check slots that haven’t run yet appear as ‘-’ like failures to connect.

Begin - Marks the start of a VXID

The first record of a VXID transaction.

The format is:

%s %d %s [%u]
|  |  |   |
|  |  |   +- Task sub-level
|  |  +----- Reason
|  +-------- Parent vxid
+----------- Type ("sess", "req" or "bereq")
BereqAcct - Backend request accounting

Contains byte counters from backend request processing.

The format is:

%d %d %d %d %d %d
|  |  |  |  |  |
|  |  |  |  |  +- Total bytes received
|  |  |  |  +---- Body bytes received
|  |  |  +------- Header bytes received
|  |  +---------- Total bytes transmitted
|  +------------- Body bytes transmitted
+---------------- Header bytes transmitted
BereqHeader - Backend request header

HTTP header contents.

The format is:

%s: %s
|   |
|   +- Header value
+----- Header name

NOTE: HTTP header fields are free form records and not strictly made of 2 fields. Accessing a specific header with the prefix notation helps treating the header value as a single string.

BereqMethod - Backend request method

The HTTP request method used.

BereqProtocol - Backend request protocol

The HTTP protocol version information.

BereqURL - Backend request URL

The HTTP request URL.

BereqUnset - Backend request unset header

HTTP header contents.

The format is:

%s: %s
|   |
|   +- Header value
+----- Header name

NOTE: HTTP header fields are free form records and not strictly made of 2 fields. Accessing a specific header with the prefix notation helps treating the header value as a single string.

BerespHeader - Backend response header

HTTP header contents.

The format is:

%s: %s
|   |
|   +- Header value
+----- Header name

NOTE: HTTP header fields are free form records and not strictly made of 2 fields. Accessing a specific header with the prefix notation helps treating the header value as a single string.

BerespProtocol - Backend response protocol

The HTTP protocol version information.

BerespReason - Backend response reason

The HTTP response reason string.

BerespStatus - Backend response status

The HTTP response status code.

BerespUnset - Backend response unset header

HTTP header contents.

The format is:

%s: %s
|   |
|   +- Header value
+----- Header name

NOTE: HTTP header fields are free form records and not strictly made of 2 fields. Accessing a specific header with the prefix notation helps treating the header value as a single string.

BogoHeader - Bogus HTTP received

Contains the first 20 characters of received HTTP headers we could not make sense of. Applies to both req.http and beresp.http.

CLI - CLI communication

CLI communication between varnishd master and child process.

Debug - Debug messages

Debug messages can normally be ignored, but are sometimes helpful during trouble-shooting. Most debug messages must be explicitly enabled with parameters.

Debug messages may be added, changed or removed without prior notice and shouldn’t be considered stable.

NB: This log record is masked by default.

ESI_xmlerror - ESI parser error or warning message

An error or warning was generated during parsing of an ESI object. The log record describes the problem encountered.

End - Marks the end of a VXID

The last record of a VXID transaction.

Error - Error messages

Error messages are stuff you probably want to know.

ExpBan - Object evicted due to ban

Logs the VXID when an object is banned.

ExpKill - Object expiry event

Logs events related to object expiry. The events are:

EXP_Rearm

Logged when the expiry time of an object changes.

EXP_Inbox

Logged when the expiry thread picks an object from the inbox for processing.

EXP_Kill

Logged when the expiry thread kills an object from the inbox.

EXP_When

Logged when the expiry thread moves an object on the binheap.

EXP_Expired

Logged when the expiry thread expires an object.

LRU_Cand

Logged when an object is evaluated for LRU force expiry.

LRU

Logged when an object is force expired due to LRU.

LRU_Fail

Logged when no suitable candidate object is found for LRU force expiry.

The format is:

EXP_Rearm p=%p E=%f e=%f f=0x%x
EXP_Inbox p=%p e=%f f=0x%x
EXP_Kill p=%p e=%f f=0x%x
EXP_When p=%p e=%f f=0x%x
EXP_Expired x=%u t=%f
LRU_Cand p=%p f=0x%x r=%d
LRU x=%u
LRU_Fail

Legend:
p=%p         Objcore pointer
t=%f         Remaining TTL (s)
e=%f         Expiry time (unix epoch)
E=%f         Old expiry time (unix epoch)
f=0x%x       Objcore flags
r=%d         Objcore refcount
x=%u         Object VXID
FetchError - Error while fetching object

Logs the error message of a failed fetch operation.

Error messages should be self-explanatory, yet the http connection (HTC) class of errors is reported with these symbols:

  • junk (-5): Received unexpected data

  • close (-4): Connection closed

  • timeout (-3): Timed out

  • overflow (-2): Buffer/workspace too small

  • eof (-1): Unexpected end of input

  • empty (0): Empty response

  • more (1): More data required

  • complete (2): Data complete (no error)

  • idle (3): Connection was closed while idle

Notice that some HTC errors are never emitted.

Fetch_Body - Body fetched from backend

Ready to fetch body from backend.

The format is:

%d %s %s
|  |  |
|  |  +---- 'stream' or '-'
|  +------- Text description of body fetch mode
+---------- Body fetch mode
Filters - Body filters

List of filters applied to the body

Gzip - G(un)zip performed on object

A Gzip record is emitted for each instance of gzip or gunzip work performed. Worst case, an ESI transaction stored in gzip’ed objects but delivered gunziped, will run into many of these.

The format is:

%c %c %c %d %d %d %d %d
|  |  |  |  |  |  |  |
|  |  |  |  |  |  |  +- Bit length of compressed data
|  |  |  |  |  |  +---- Bit location of 'last' bit
|  |  |  |  |  +------- Bit location of first deflate block
|  |  |  |  +---------- Bytes output
|  |  |  +------------- Bytes input
|  |  +---------------- 'E': ESI, '-': Plain object
|  +------------------- 'F': Fetch, 'D': Deliver
+---------------------- 'G': Gzip, 'U': Gunzip, 'u': Gunzip-test

Examples:

U F E 182 159 80 80 1392
G F E 159 173 80 1304 1314
H2RxBody - Received HTTP2 frame body

Binary data

H2RxHdr - Received HTTP2 frame header

Binary data

H2TxBody - Transmitted HTTP2 frame body

Binary data

H2TxHdr - Transmitted HTTP2 frame header

Binary data

Hash - Value added to hash

This value was added to the object lookup hash.

NB: This log record is masked by default.

Hit - Hit object in cache

Object looked up in cache.

The format is:

%u %f %f %f [%u [%u]]
|  |  |  |   |   |
|  |  |  |   |   +- Content length
|  |  |  |   +----- Fetched so far
|  |  |  +--------- Keep period
|  |  +------------ Grace period
|  +--------------- Remaining TTL
+------------------ VXID of the object
HitMiss - Hit for miss object in cache.

Hit-for-miss object looked up in cache.

The format is:

%u %f
|  |
|  +- Remaining TTL
+---- VXID of the object
HitPass - Hit for pass object in cache.

Hit-for-pass object looked up in cache.

The format is:

%u %f
|  |
|  +- Remaining TTL
+---- VXID of the object
HttpGarbage - Unparseable HTTP request

Logs the content of unparseable HTTP requests.

Length - Size of object body

Logs the size of a fetch object body.

Link - Links to a child VXID

Links this VXID to any child VXID it initiates.

The format is:

%s %d %s [%u]
|  |  |   |
|  |  |   +- Child task sub-level
|  |  +----- Reason
|  +-------- Child vxid
+----------- Child type ("sess", "req" or "bereq")
LostHeader - Failed attempt to set HTTP header

Logs the header name of a failed HTTP header operation due to resource exhaustion or configured limits.

Notice - Informational messages about request handling

Informational log messages on events occurred during request handling.

The format is:

%s: %s
|   |
|   +- Short description of the notice message
+----- Manual page containing the detailed description

See the NOTICE MESSAGES section below or the individual VMOD manual pages for detailed information of notice messages.

ObjHeader - Object header

HTTP header contents.

The format is:

%s: %s
|   |
|   +- Header value
+----- Header name

NOTE: HTTP header fields are free form records and not strictly made of 2 fields. Accessing a specific header with the prefix notation helps treating the header value as a single string.

ObjProtocol - Object protocol

The HTTP protocol version information.

ObjReason - Object reason

The HTTP response reason string.

ObjStatus - Object status

The HTTP response status code.

ObjUnset - Object unset header

HTTP header contents.

The format is:

%s: %s
|   |
|   +- Header value
+----- Header name

NOTE: HTTP header fields are free form records and not strictly made of 2 fields. Accessing a specific header with the prefix notation helps treating the header value as a single string.

PipeAcct - Pipe byte counts

Contains byte counters for pipe sessions.

The format is:

%d %d %d %d
|  |  |  |
|  |  |  +------- Piped bytes to client
|  |  +---------- Piped bytes from client
|  +------------- Backend request headers
+---------------- Client request headers
Proxy - PROXY protocol information

PROXY protocol information.

The format is:

%d %s %d %s %d
|  |  |  |  |
|  |  |  |  +- server port
|  |  |  +---- server ip
|  |  +------- client port
|  +---------- client ip
+------------- PROXY protocol version

All fields are "local" for PROXY local connections (command 0x0)
ProxyGarbage - Unparseable PROXY request

A PROXY protocol header was unparseable.

ReqAcct - Request handling byte counts

Contains byte counts for the request handling. The body bytes count includes transmission overhead (ie: chunked encoding). ESI sub-requests show the body bytes this ESI fragment including any subfragments contributed to the top level request. The format is:

%d %d %d %d %d %d
|  |  |  |  |  |
|  |  |  |  |  +- Total bytes transmitted
|  |  |  |  +---- Body bytes transmitted
|  |  |  +------- Header bytes transmitted
|  |  +---------- Total bytes received
|  +------------- Body bytes received
+---------------- Header bytes received
ReqHeader - Client request header

HTTP header contents.

The format is:

%s: %s
|   |
|   +- Header value
+----- Header name

NOTE: HTTP header fields are free form records and not strictly made of 2 fields. Accessing a specific header with the prefix notation helps treating the header value as a single string.

ReqMethod - Client request method

The HTTP request method used.

ReqProtocol - Client request protocol

The HTTP protocol version information.

ReqStart - Client request start

Start of request processing. Logs the client address, port number and listener endpoint name (from the -a command-line argument).

The format is:

%s %s %s
|  |  |
|  |  +-- Listener name (from -a)
|  +----- Client Port number (0 for Unix domain sockets)
+-------- Client IP4/6 address (0.0.0.0 for UDS)
ReqURL - Client request URL

The HTTP request URL.

ReqUnset - Client request unset header

HTTP header contents.

The format is:

%s: %s
|   |
|   +- Header value
+----- Header name

NOTE: HTTP header fields are free form records and not strictly made of 2 fields. Accessing a specific header with the prefix notation helps treating the header value as a single string.

RespHeader - Client response header

HTTP header contents.

The format is:

%s: %s
|   |
|   +- Header value
+----- Header name

NOTE: HTTP header fields are free form records and not strictly made of 2 fields. Accessing a specific header with the prefix notation helps treating the header value as a single string.

RespProtocol - Client response protocol

The HTTP protocol version information.

RespReason - Client response reason

The HTTP response reason string.

RespStatus - Client response status

The HTTP response status code.

RespUnset - Client response unset header

HTTP header contents.

The format is:

%s: %s
|   |
|   +- Header value
+----- Header name

NOTE: HTTP header fields are free form records and not strictly made of 2 fields. Accessing a specific header with the prefix notation helps treating the header value as a single string.

SessClose - Client connection closed

SessClose is the last record for any client connection.

The format is:

%s %f
|  |
|  +- How long the session was open
+---- Why the connection closed
SessError - Client connection accept failed

Accepting a client connection has failed.

The format is:

%s %s %s %d %d %s
|  |  |  |  |  |
|  |  |  |  |  +- Detailed error message
|  |  |  |  +---- Error Number (errno) from accept(2)
|  |  |  +------- File descriptor number
|  |  +---------- Local TCP port / 0 for UDS
|  +------------- Local IPv4/6 address / 0.0.0.0 for UDS
+---------------- Socket name (from -a argument)
SessOpen - Client connection opened

The first record for a client connection, with the socket-endpoints of the connection.

The format is:

%s %d %s %s %s %f %d
|  |  |  |  |  |  |
|  |  |  |  |  |  +- File descriptor number
|  |  |  |  |  +---- Session start time (unix epoch)
|  |  |  |  +------- Local TCP port / 0 for UDS
|  |  |  +---------- Local IPv4/6 address / 0.0.0.0 for UDS
|  |  +------------- Socket name (from -a argument)
|  +---------------- Remote TCP port / 0 for UDS
+------------------- Remote IPv4/6 address / 0.0.0.0 for UDS
Storage - Where object is stored

Type and name of the storage backend the object is stored in.

The format is:

%s %s
|  |
|  +- Name of storage backend
+---- Type ("malloc", "file", "persistent" etc.)
TTL - TTL set on object

A TTL record is emitted whenever the ttl, grace or keep values for an object is set as well as whether the object is cacheable or not.

The format is:

%s %d %d %d %d [ %d %d %u %u ] %s
|  |  |  |  |    |  |  |  |    |
|  |  |  |  |    |  |  |  |    +- "cacheable" or "uncacheable"
|  |  |  |  |    |  |  |  +------ Max-Age from Cache-Control header
|  |  |  |  |    |  |  +--------- Expires header
|  |  |  |  |    |  +------------ Date header
|  |  |  |  |    +--------------- Age (incl Age: header value)
|  |  |  |  +-------------------- Reference time for TTL
|  |  |  +----------------------- Keep
|  |  +-------------------------- Grace
|  +----------------------------- TTL
+-------------------------------- "RFC", "VCL" or "HFP"

The four optional fields are only present in “RFC” headers.

Examples:

RFC 60 10 -1 1312966109 1312966109 1312966109 0 60 cacheable
VCL 120 10 0 1312966111 uncacheable
HFP 2 0 0 1312966113 uncacheable
Timestamp - Timing information

Contains timing information for the Varnish worker threads.

Time stamps are issued by Varnish on certain events, and show the absolute time of the event, the time spent since the start of the work unit, and the time spent since the last timestamp was logged. See the TIMESTAMPS section below for information about the individual time stamps.

The format is:

%s: %f %f %f
|   |  |  |
|   |  |  +- Time since last timestamp
|   |  +---- Time since start of work unit
|   +------- Absolute time of event
+----------- Event label
VCL_Error - VCL execution error message

Logs error messages generated during VCL execution.

VCL_Log - Log statement from VCL

User generated log messages insert from VCL through std.log()

VCL_acl - VCL ACL check results

ACLs with the +log flag emits this record with the result.

The format is:

%s %s [%s [fixed: %s]]
|  |   |          |
|  |   |          +- Fixed entry (see acl +pedantic flag)
|  |   +------------ Matching entry (only for MATCH)
|  +---------------- Name of the ACL
+-------------------- MATCH or NO_MATCH

MATCH denotes an ACL match NO_MATCH denotes that a checked ACL has not matched

VCL_call - VCL method called

Logs the VCL method name when a VCL method is called.

VCL_return - VCL method return value

Logs the VCL method terminating statement.

VCL_trace - VCL trace data

Logs VCL execution trace data.

The format is:

%s %u %u.%u.%u
|  |  |  |  |
|  |  |  |  +- VCL program line position
|  |  |  +---- VCL program line number
|  |  +------- VCL program source index
|  +---------- VCL trace point index
+------------- VCL configname

NB: This log record is masked by default.

VCL_use - VCL in use

Records the name of the VCL being used.

The format is:

%s [ %s %s ]
|    |  |
|    |  +- Name of label used to find it
|    +---- "via"
+--------- Name of VCL put in use
VSL - VSL API warnings and error message

Warnings and error messages generated by the VSL API while reading the shared memory log.

VdpAcct - Deliver filter accounting

Contains name of VDP and statistics.

The format is:

%s %d %d
|  |  |
|  |  +- Total bytes produced
|  +---- Number of calls made
+------- Name of filter

NB: This log record is masked by default.

VfpAcct - Fetch filter accounting

Contains name of VFP and statistics.

The format is:

%s %d %d
|  |  |
|  |  +- Total bytes produced
|  +---- Number of calls made
+------- Name of filter

NB: This log record is masked by default.

Witness - Lock order witness records

Diagnostic recording of locking order.

WorkThread - Logs thread start/stop events

Logs worker thread creation and termination events.

The format is:

%p %s
|  |
|  +- [start|end]
+---- Worker struct pointer

NB: This log record is masked by default.

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() function. 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.

Reset

The client closed its connection, reset its stream or caused a stream error that forced Varnish to reset the stream. Request processing is interrupted and considered failed, with a 408 “Request Timeout” status code.

Pipe handling timestamps

The following timestamps are client timestamps specific to pipe transactions:

Pipe

Opened a pipe to the backend and forwarded the request.

PipeSess

The pipe session has finished.

The following timestamps change meaning in a pipe transaction:

Process

Processing finished, ready to begin the pipe delivery.

Backend fetch timestamps

Start

Start of the backend fetch processing.

Fetch

Came off vcl_backend_fetch ready to send the backend request.

Connected

Successfully established a backend connection, or selected a recycled connection from the pool.

Bereq

Backend request sent.

Beresp

Backend response headers received.

Process

Processing finished, ready to fetch the response body.

BerespBody

Backend response body received.

Retry

Backend request is being retried.

Error

Backend request failed to vcl_backend_error.

NOTICE MESSAGES

Notice messages contain informational messages about the handling of a request. These can be exceptional circumstances encountered that causes deviation from the normal handling. The messages are prefixed with vsl: for core Varnish generated messages, and VMOD authors are encouraged to use vmod_<name>: for their own notice messages. This matches the name of the manual page where detailed descriptions of notice messages are expected.

The core messages are described below.

Conditional fetch wait for streaming object

The backend answered 304 Not Modified on a conditional fetch using an object that has not yet been fully fetched as the stale template object. This can only happen when the TTL of the object is less than the time it takes to fetch it. The fetch is halted until the stale object is fully fetched, upon which the new object is created as normal. While waiting, any grace time on the stale object will be in effect.

High number of variants

Objects are primarily looked up from an index using the hash key computed from the hash_data() VCL function. When variants are involved, that is to say when a backend response was stored with a Vary header, a secondary lookup is performed but it is not indexed. As the number of variants for a given key increases, this can slow cache lookups down, and since this happens under a lock, this can greatly increase lock contention, even more so for frequently requested objects. Variants should therefore be used sparingly on cacheable responses, but since they can originate from either VCL or origin servers, this notice should help identify problematic resources.

HISTORY

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

SEE ALSO