Ubuntu Manpage: vsl-query - Varnish VSL Query Expressions

NAME

       vsl-query - Varnish VSL Query Expressions

OVERVIEW

       The  Varnish  VSL  Query  Expressions extracts transactions from the Varnish shared memory
       log, and perform queries on the transactions before reporting matches.

       A transaction is a set of log lines that belongs together, e.g.  a  client  request  or  a
       backend  request.  The  API  monitors the log, and collects all log records that make up a
       transaction before reporting on  that  transaction.  Transactions  can  also  be  grouped,
       meaning  backend  transactions  are  reported  together  with  the client transaction that
       initiated it.

       A query is run on a group of transactions. A query expression is true if there  is  a  log
       record  within the group that satisfies the condition. It is false only if none of the log
       records  satisfies  the  condition.  Query  expressions  can  be  combined  using  boolean
       functions.   In addition to log records, it is possible to query transaction ids (vxid) in
       query.

GROUPING

When grouping transactions, there is a hierarchy structure showing which transaction
initiated what. The level increases by one on an 'initiated by' relation, so for example a
backend transaction will have one higher level than the client transaction that initiated
it on a cache miss. Request restart transactions don't get their level increased to make
it predictable.

Levels start counting at 1, except when using raw where it will always be 0.

The grouping modes are:

• session

All transactions initiated by a client connection are reported together. Client
connections are open ended when using HTTP keep-alives, so it is undefined when the
session will be reported. If the transaction timeout period is exceeded an incomplete
session will be reported. Non-transactional data (vxid == 0) is not reported.

• request

Transactions are grouped by request, where the set will include the request itself as
well as any backend requests or ESI-subrequests. Session data and non-transactional
data (vxid == 0) is not reported.

• vxid

Transactions are not grouped, so each vxid is reported in its entirety. Sessions,
requests, ESI-requests and backend requests are all reported individually.
Non-transactional data is not reported (vxid == 0). This is the default.

• raw

Every log record will make up a transaction of its own. All data, including
non-transactional data will be reported.

Transaction Hierarchy
Example transaction hierarchy using request grouping mode

Lvl 1: Client request (cache miss)
Lvl 2: Backend request
Lvl 2: ESI subrequest (cache miss)
Lvl 3: Backend request
Lvl 3: Backend request (VCL restart)
Lvl 3: ESI subrequest (cache miss)
Lvl 4: Backend request
Lvl 2: ESI subrequest (cache hit)

MEMORY USAGE

       The API will use pointers to shared memory log data as long as  possible  to  keep  memory
       usage  at  a  minimum.  But  as  the  shared  memory  log  is a ring buffer, data will get
       overwritten eventually, so the API creates  local  copies  of  referenced  log  data  when
       varnishd comes close to overwriting still unreported content.

       This  process  avoids loss of log data in many scenarios, but it is not failsafe: Overruns
       where varnishd "overtakes" the log reader process in the ring buffer can still happen when
       API clients cannot keep up reading and/or copying, for instance due to output blocking.

       Though  being  unrelated  to  grouping  in  principle, copying of log data is particularly
       relevant for session grouping together with long lasting client  connections  -  for  this
       grouping,  the logging API client process is likely to consume relevant amounts of memory.
       As the vxid grouping also logs (potentially long lasting) sessions, it is also  likely  to
       require memory for copies of log entries, but far less than session grouping.

QUERY LANGUAGE

A query expression consists of record selection criteria, and optionally an operator and a
value to match against the selected records.

Additionally, a query expression can occur on the transaction itself rather than log
records belonging to the transaction.

vxid <numerical operator> <integer>

A vxid query allows you to directly target a specific transacion, whose id can be obtained
from an X-Varnish HTTP header, the default "guru meditation" error page, or Begin and Link
log records.

A query must fit on a single line, but it is possible to pass multiple queries at once,
one query per line. Empty lines are ignored, and the list of queries is treated as if the
'or' operator was used to combine them.

For example this list of queries:

# catch varnish errors
*Error

# catch backend errors
BerespStatus >= 500

is identical to this query:

(*Error) or (BerespStatus >= 500)

Comments can be used and will be ignored, they start with the '#' character, which may be
more useful when the query is read from a file.

For very long queries that couldn't easily be split into multiple queries it is possible
to break them into multiple lines with a backslash preceding an end of line.

For example this query:

BerespStatus >= 500

is identical to this query:

BerespStatus \
>= \
500

A backslash-newline sequence doesn't continue a comment on the next line and isn't allowed
in a quoted string.

Record selection criteria
The record selection criteria determines what kind records from the transaction group the
expression applies to. Syntax:

{level}taglist:record-prefix[field]

Taglist is mandatory, the other components are optional.

The level limits the expression to a transaction at that level. If left unspecified, the
expression is applied to transactions at all levels. Level is a positive integer or zero.
If level is followed by a '+' character, it expresses greater than or equal. If level is
followed by a '-', it expresses less than or equal.

The taglist is a comma-separated list of VSL record tags that this expression should be
checked against. Each list element can be a tag name or a tag glob. Globs allow a '*'
either in the beginning of the name or at the end, and will select all tags that match
either the prefix or subscript. A single '*' will select all tags.

The record prefix will further limit the matches to those records that has this prefix as
their first part of the record content followed by a colon. The part of the log record
matched against will then be limited to what follows the prefix and colon. This is useful
when matching against specific HTTP headers. The record prefix matching is done case
insensitive.

The field will, if present, treat the log record as a white space separated list of
fields, and only the nth part of the record will be matched against. Fields start counting
at 1.

An expression using only a record selection criteria will be true if there is any record
in the transaction group that is selected by the criteria.

Operators
The following matching operators are available:

• == != < <= > >=

Numerical comparison. The record contents will be converted to either an integer or a
float before comparison, depending on the type of the operand.

• eq ne

String comparison. 'eq' tests string equality, 'ne' tests for not equality.

• ~ !~

Regular expression matching. '~' is a positive match, '!~' is a non-match.

Operand
The operand is the value the selected records will be matched against.

An operand can be quoted or unquoted. Quotes can be either single or double quotes, and
for quoted operands a backslash can be used to escape the quotes.

Unquoted operands can only consist of the following characters:

a-z A-Z 0-9 + - _ . *

The following types of operands are available:

• Integer

A number without any fractional part, valid for the numerical comparison operators. The
integer type is used when the operand does not contain any period (.) nor exponent (e)
characters. However if the record evaluates as a float, only its integral part is used
for the comparison.

• Float

A number with a fractional part, valid for the numerical comparison operators. The float
type is used when the operand does contain a period (.) or exponent (e) character.

• String

A sequence of characters, valid for the string equality operators.

• Regular expression

A PCRE regular expression. Valid for the regular expression operators.

Boolean functions
Query expressions can be linked together using boolean functions. The following are
available, in decreasing precedence:

• not <expr>

Inverts the result of <expr>

• <expr1> and <expr2>

True only if both expr1 and expr2 are true

• <expr1> or <expr2>

True if either of expr1 or expr2 is true

Expressions can be grouped using parenthesis.

QUERY EXPRESSION EXAMPLES

       • Transaction group contains a request URL that equals to "/foo"

            ReqURL eq "/foo"

       • Transaction group contains a request cookie header

            ReqHeader:cookie

       • Transaction group doesn't contain a request cookie header

            not ReqHeader:cookie

       • Client request where internal handling took more than 800ms.:

            Timestamp:Process[2] > 0.8

       • Transaction  group  contains  a  request  user-agent header that contains "iPod" and the
         request delivery time exceeds 1 second

            ReqHeader:user-agent ~ "iPod" and Timestamp:Resp[2] > 1.

       • Transaction group contains a backend response status larger than or equal to 500

            BerespStatus >= 500

       • Transaction group contains a request response status of 304, but where the  request  did
         not contain an if-modified-since header

            RespStatus == 304 and not ReqHeader:if-modified-since

       • Transactions  that  have  had  backend  failures  or  long  delivery  time  on their ESI
         subrequests. (Assumes request grouping mode).

            BerespStatus >= 500 or {2+}Timestamp:Process[2] > 1.

       • Log non-transactional errors. (Assumes raw grouping mode).

            vxid == 0 and Error

HISTORY

       This document was initially written by Martin Blix Grydeland and amended by others.

COPYRIGHT

       This document is licensed under the same  licence  as  Varnish  itself.  See  LICENCE  for
       details.

       • Copyright (c) 2006 Verdens Gang AS

       • Copyright (c) 2006-2015 Varnish Software AS

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