Provided by: varnish_6.1.1-1_amd64 bug

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.

          <record selection criteria> <operator> <operand>

       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.

   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 (.) characters.

       · 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 (.) 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 written by Martin Blix Grydeland.

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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