mmv(5) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | FILE FORMAT | SEE ALSO | COLOPHON

MMV(5)                     File Formats Manual                    MMV(5)

NAME         top

       mmv - Memory Mapped Values for Performance Co-Pilot

SYNOPSIS         top

       $PCP_TMP_DIR/mmv/<file>

DESCRIPTION         top

       The files in $PCP_TMP_DIR/mmv are generated either by the
       mmv_stats_init(3) and mmv_stats2_init(3) functions from the
       libpcp_mmv library, or by a native language module such as
       Parfait (Java), Speed (Golang) or Hornet (Rust).

       There could be multiple files in this directory, each file
       representing a single source of the performance metrics.  The
       metrics are harvested by pmdammv(1) which exports them to the
       rest of the Performance Co-Pilot infrastructure.

FILE FORMAT         top

       Each file starts with the following header:

                 ┌───────┬────────┬──────────────────────────┐
                 │Offset │ Length │           Name           │
                 ├───────┼────────┼──────────────────────────┤
                 │   0   │   4    │ tag == "MMV\0"           │
                 ├───────┼────────┼──────────────────────────┤
                 │   4   │   4    │ Version (1 or 2)         │
                 ├───────┼────────┼──────────────────────────┤
                 │   8   │   8    │ Generation 1             │
                 ├───────┼────────┼──────────────────────────┤
                 │  16   │   8    │ Generation 2             │
                 ├───────┼────────┼──────────────────────────┤
                 │  24   │   4    │ Number of TOC entries    │
                 ├───────┼────────┼──────────────────────────┤
                 │  28   │   4    │ Flags                    │
                 ├───────┼────────┼──────────────────────────┤
                 │  32   │   4    │ Process identifier (PID) │
                 ├───────┼────────┼──────────────────────────┤
                 │  36   │   4    │ Cluster identifier       │
                 └───────┴────────┴──────────────────────────┘
       The version number specifies which mapping layout format is in
       use.  There are two, both are very similar, as described below.
       The sole purpose of the MMV version 2 format is to allow the use
       of longer metric and instance names.  If names longer than
       MMV_NAMEMAX are not in use, it is best to use MMV version 1
       format as this allows older versions of PCP to also consume the
       data.  Support for v2 format was added in the pcp-3.11.4 release.

       The generation numbers are timestamps at the time of file
       creation, and must match for the file to be considered by the MMV
       PMDA.

       The flags can specify ways in which the client would like the MMV
       PMDA to behave - e.g. the MMV_FLAG_PROCESS flag specifies that
       only if the process identified by PID is currently running should
       those values be exported.

       Finally, if set, the cluster identifier is a hint to the MMV PMDA
       as to what cluster should be used with this application when
       forming the individual metric identifiers.  A performance metric
       identifier (see PMDA(3)) consists of the PMDA domain number, the
       cluster number, and the individual item numbers described in the
       Metrics section.

       The header is followed by at least 2 TOC sections: one section
       for metrics and another for values.  The TOC section has the
       following format:

        ┌───────┬────────┬─────────────────────────────────────────────┐
        │Offset │ Length │                    Value                    │
        ├───────┼────────┼─────────────────────────────────────────────┤
        │  0    │   4    │ Section Type (see mmv_stats.h)              │
        ├───────┼────────┼─────────────────────────────────────────────┤
        │  4    │   4    │ Number of entries in the section            │
        ├───────┼────────┼─────────────────────────────────────────────┤
        │  8    │   8    │ Section's offset from the start of the file │
        └───────┴────────┴─────────────────────────────────────────────┘
       The section types are:

              1: Indoms (instance domain definitions)

              2: Instances

              3: Metrics (metric definitions)

              4: Values

              5: String

              6: Labels

       The only mandatory sections are Metrics and Values.  Indoms and
       Instances sections of either version only appear if there are
       metrics with multiple instances.  String sections only appear if
       there are metrics with string values, when Metrics or Indoms are
       defined with help text, or in v2 MMV format where metric names
       and instance names are stored in string sections (providing
       significantly more space than v1 MMV format for these names).
       Label sections only appear if there are metrics annotated with
       labels (name/value pairs).  Labels are supported in v3 MMV
       format.

       The entries in the Indoms sections have the following format:

           ┌───────┬────────┬───────────────────────────────────────┐
           │Offset │ Length │                 Value                 │
           ├───────┼────────┼───────────────────────────────────────┤
           │   0   │   4    │ Unique serial number for this domain  │
           ├───────┼────────┼───────────────────────────────────────┤
           │   4   │   4    │ Number of entries in the domain       │
           ├───────┼────────┼───────────────────────────────────────┤
           │   8   │   8    │ Offset to first Instance or Instance2 │
           ├───────┼────────┼───────────────────────────────────────┤
           │  16   │   8    │ Short help text offset                │
           ├───────┼────────┼───────────────────────────────────────┤
           │  24   │   8    │ Long help text offset                 │
           └───────┴────────┴───────────────────────────────────────┘
       The entries in the Instances (v1) section have the following
       format:

               ┌───────┬────────┬───────────────────────────────┐
               │Offset │ Length │             Value             │
               ├───────┼────────┼───────────────────────────────┤
               │   0   │    8   │ Offset into the indom section │
               ├───────┼────────┼───────────────────────────────┤
               │   8   │    4   │ Unused padding (zero filled)  │
               ├───────┼────────┼───────────────────────────────┤
               │  12   │    4   │ Internal instance identifier  │
               ├───────┼────────┼───────────────────────────────┤
               │  16   │   64   │ External instance identifier  │
               └───────┴────────┴───────────────────────────────┘
       The entries in the Instances (v2) section have the following
       format:

        ┌───────┬────────┬────────────────────────────────────────────┐
        │Offset │ Length │                   Value                    │
        ├───────┼────────┼────────────────────────────────────────────┤
        │   0   │   8    │ Offset into the indom section              │
        ├───────┼────────┼────────────────────────────────────────────┤
        │   8   │   4    │ Unused padding (zero filled)               │
        ├───────┼────────┼────────────────────────────────────────────┤
        │  12   │   4    │ Internal instance identifier               │
        ├───────┼────────┼────────────────────────────────────────────┤
        │  16   │   8    │ External instance identifier string offset │
        └───────┴────────┴────────────────────────────────────────────┘
       The entries in the Metrics (v1) section have the following
       format:

               ┌───────┬────────┬───────────────────────────────┐
               │Offset │ Length │             Value             │
               ├───────┼────────┼───────────────────────────────┤
               │   0   │   64   │ Metric Name                   │
               ├───────┼────────┼───────────────────────────────┤
               │  64   │    4   │ Metric Item (see PMDA(3))     │
               ├───────┼────────┼───────────────────────────────┤
               │  68   │    4   │ Metric Type (see mmv_stats.h) │
               ├───────┼────────┼───────────────────────────────┤
               │  72   │    4   │ Semantics (see PMAPI(3))      │
               ├───────┼────────┼───────────────────────────────┤
               │  76   │    4   │ Dimensions (see PMAPI(3))     │
               ├───────┼────────┼───────────────────────────────┤
               │  80   │    4   │ Instance Domain ID            │
               ├───────┼────────┼───────────────────────────────┤
               │  84   │    4   │ Unused padding (zero filled)  │
               ├───────┼────────┼───────────────────────────────┤
               │  88   │    8   │ Short help text offset        │
               ├───────┼────────┼───────────────────────────────┤
               │  96   │    8   │ Long help text offset         │
               └───────┴────────┴───────────────────────────────┘
       The entries in the Metrics (v2) section have the following
       format:

               ┌───────┬────────┬───────────────────────────────┐
               │Offset │ Length │             Value             │
               ├───────┼────────┼───────────────────────────────┤
               │   0   │   8    │ Metric Name string offset     │
               ├───────┼────────┼───────────────────────────────┤
               │   8   │   4    │ Metric Item (see PMDA(3))     │
               ├───────┼────────┼───────────────────────────────┤
               │  12   │   4    │ Metric Type (see mmv_stats.h) │
               ├───────┼────────┼───────────────────────────────┤
               │  16   │   4    │ Semantics (see PMAPI(3))      │
               ├───────┼────────┼───────────────────────────────┤
               │  20   │   4    │ Dimensions (see PMAPI(3))     │
               ├───────┼────────┼───────────────────────────────┤
               │  24   │   4    │ Instance Domain ID            │
               ├───────┼────────┼───────────────────────────────┤
               │  28   │   4    │ Unused padding (zero filled)  │
               ├───────┼────────┼───────────────────────────────┤
               │  32   │   8    │ Short help text offset        │
               ├───────┼────────┼───────────────────────────────┤
               │  40   │   8    │ Long help text offset         │
               └───────┴────────┴───────────────────────────────┘
       The entries in the Values section have the following format:

            ┌───────┬────────┬────────────────────────────────────┐
            │Offset │ Length │               Value                │
            ├───────┼────────┼────────────────────────────────────┤
            │   0   │   8    │ pmAtomValue (see PMAPI(3))         │
            ├───────┼────────┼────────────────────────────────────┤
            │   8   │   8    │ Extra space for STRING and ELAPSED │
            ├───────┼────────┼────────────────────────────────────┤
            │  16   │   8    │ Offset into the Metrics section    │
            ├───────┼────────┼────────────────────────────────────┤
            │  24   │   8    │ Offset into the Instances section  │
            └───────┴────────┴────────────────────────────────────┘
       Each entry in the strings section is a 256 byte character array,
       containing a single NULL-terminated character string.  So each
       string has a maximum length of 256 bytes, which includes the
       terminating NULL.

       The entries in the Labels (v3) section have the following format:

  ┌───────┬────────┬──────────────────────────────────────────────────────────┐
  │Offset │ Length │                          Value                           │
  ├───────┼────────┼──────────────────────────────────────────────────────────┤
  │   0   │    4   │ Flags (PM_LABEL_[CLUSTER|ITEM|INDOM|INSTANCES]|OPTIONAL) │
  ├───────┼────────┼──────────────────────────────────────────────────────────┤
  │   4   │    4   │ Identifier for given type (indom, cluster or item)       │
  ├───────┼────────┼──────────────────────────────────────────────────────────┤
  │   8   │    4   │ Internal Instance or PM_IN_NULL                          │
  ├───────┼────────┼──────────────────────────────────────────────────────────┤
  │  12   │  244   │ Payload (Name and Value JSONB String)                    │
  └───────┴────────┴──────────────────────────────────────────────────────────┘
       Each entry in the payload is a 244 byte (maximum) character
       array, containing a single NULL-terminated name:value pair in
       JSON format.  Insignificant whitespace must not be present.
       Label names consist only of alphanumeric characters or
       underscores, and must begin with an alphabetic.  Upper and lower
       case characters are considered distinct.

SEE ALSO         top

       PCPIntro(1), pmdammv(1), PMAPI(3), mmv_stats_init(3), pcp.conf(5)
       and pcp.env(5).

COLOPHON         top

       This page is part of the PCP (Performance Co-Pilot) project.
       Information about the project can be found at 
       ⟨http://www.pcp.io/⟩.  If you have a bug report for this manual
       page, send it to pcp@groups.io.  This page was obtained from the
       project's upstream Git repository
       ⟨https://github.com/performancecopilot/pcp.git⟩ on 2021-08-27.
       (At that time, the date of the most recent commit that was found
       in the repository was 2021-08-27.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

Performance Co-Pilot                                              MMV(5)

Pages that refer to this page: pmdammv(1)mmv_inc_value(3)mmv_lookup_value_desc(3)mmv_stats_init(3)mmv_stats_registry(3)