Provided by: pcp_6.2.0-1.1build4_amd64 
NAME
LOGARCHIVE - Performance Co-Pilot archive formats
DESCRIPTION
Performance Co-Pilot (PCP) archives store historical values about arbitrary metrics
recorded from a single host. Archives are machine independent and self-contained - all
metric data and metadata required for off-line or off-site analysis is held within an
archive.
The format is stable in order to allow long-term historical storage and processing by
PMAPI(3) client tools. However some format variants are supported over time, and
currently Versions 2 and 3 are supported. The mandate is that PCP will provide long-term
backwards compatibility, so an archive created on any version of PCP can be read on that
version of PCP and all subsequent versions of PCP. The exception is Version 1 that was
retired in the PCP Version 2.0 release in May 1998.
Archives may be read by most PCP client tools, using the -a/--archive NAME option, or
dumped raw by pmdumplog(1). Archives are created primarily by pmlogger(1), however they
can also be created using the LOGIMPORT(3) programming interface.
Archives may be merged, analyzed, modified and subsampled using pmlogreduce(1),
pmlogsummary(1), pmlogrewrite(1) and pmlogextract(1). In addition, PCP archives may be
examined in sets or grouped together into ``archive folios'', which are created and
managed by the mkaf(1) and pmafm(1) tools.
An archive consists of several physical files that share a common arbitrary prefix, e.g.
myarchive.
myarchive.0, myarchive.1, ...
One or more data volumes containing the metric values and any error codes
encountered during metric sampling. Typically the largest of the files and may
grow very rapidly, depending on the selection of metrics to be logged by
pmlogger(1) and the sampling intervals being used.
myarchive.meta
Information for PMAPI functions such as pmLookupName(3), pmLookupDesc(3),
pmLookupLabels(3) and pmLookupInDom(3). The metadata file may grow sporadically as
logged metrics, instance domains and labels vary over time.
myarchive.index
A temporal index, mapping timestamps to byte offsets in the other files.
COMMON FEATURES
All three types of files have a similar record-based structure, a convention of network
byte-order (big-endian) encoding, and 32-bit fields for tagging/padding for those records.
Strings are stored as 8-bit characters without assuming a specific encoding, so normally
ASCII. See also the __pmLog* types in src/include/pcp/libpcp.h.
RECORD FRAMING
The volume and .meta files are divided into self-identifying records.
┌───────┬────────┬────────────────────────────────────────────────────────────────────────┐
│Offset │ Length │ Name │
├───────┼────────┼────────────────────────────────────────────────────────────────────────┤
│ 0 │ 4 │ N, length of record, in bytes, including this field │
│ 4 │ N-8 │ record payload, usually starting with a 32-bit record type tag │
│ N-4 │ 4 │ N, length of record (again) │
└───────┴────────┴────────────────────────────────────────────────────────────────────────┘
ARCHIVE LABEL
All three types of files begin with an ``archive label'' header, which identifies the host
name, starting timestamp and timezone information; all referring to the host that was the
source of the performance data (which may be different to the host where pmlogger(1) was
running).
The ``archive label'' format differs between Version 2 and Version 3, with the latter
providing enhanced timestamps (64-bit encoding of the seconds part and nanosecond
precision) and some additional fields.
┌─────────────────────────────────────────────────────────────────────────────────────────┐
│ Version 2 │
├───────┬────────┬────────────────────────────────────────────────────────────────────────┤
│Offset │ Length │ Name │
├───────┼────────┼────────────────────────────────────────────────────────────────────────┤
│ 0 │ 4 │ tag, PM_LOG_MAGIC | PM_LOG_VERS02=0x50052602 │
│ 4 │ 4 │ process id (PID) of pmlogger process that wrote file │
│ 8 │ 4 │ archive start time, seconds part (past UNIX epoch) │
│ 12 │ 4 │ archive start time, microseconds part │
│ 16 │ 4 │ current archive volume number (or -1=.meta, -2=.index) │
│ 20 │ 64 │ name of collection host │
│ 80 │ 40 │ time zone string for collection host ($TZ environment variable) │
└───────┴────────┴────────────────────────────────────────────────────────────────────────┘
┌─────────────────────────────────────────────────────────────────────────────────────────┐
│ Version 3 │
├───────┬────────┬────────────────────────────────────────────────────────────────────────┤
│Offset │ Length │ Name │
├───────┼────────┼────────────────────────────────────────────────────────────────────────┤
│ 0 │ 4 │ tag, PM_LOG_MAGIC | PM_LOG_VERS03=0x50052603 │
│ 4 │ 4 │ PID of pmlogger process that wrote file │
│ 8 │ 8 │ archive start time, seconds part (past UNIX epoch) │
│ 16 │ 4 │ archive start time, nanoseconds part │
│ 20 │ 4 │ current archive volume number (or -1=.meta, -2=.index) │
│ 24 │ 4 │ archive feature bits │
│ 28 │ 4 │ reserved for future use │
│ 32 │ 256 │ name of collection host │
│ 288 │ 256 │ timezone string for collection host ($TZ environment variable), e.g. │
│ │ │ AEDT-11 │
│ 544 │ 256 │ timezone zoneinfo string for collection host, e.g. │
│ │ │ :Australia/Melbourne │
└───────┴────────┴────────────────────────────────────────────────────────────────────────┘
The ``archive feature bits'' are intended to encode possible future extensions or
differences to the on-disk structure or the the archive semantics. At this stage there
are no such features, but if they are introduced at some point in the future, there will
be associated PM_LOG_FEATURE_XXX macros added to the <pcp/pmapi.h> header file.
All fields, except for the ``current archive volume number'', match for all files in a
single PCP archive.
ARCHIVE VOLUME (.0, .1, ...) RECORDS
pmResult
After the archive label record, an archive volume file contains one or more records, each
providing metric values corresponding to the pmResult from one pmFetch(3) operation. The
record size may vary according to number of metrics being fetched and the number of
instances in the associated instance domains.
For Version 2 the file size is limited to 2GiB, due to storage of 32-bit byte offsets
within the temporal index. For Version 3 the file size is limited to 8191PiB, due to
storage of 62-bit byte offsets within the temporal index.
The pmResult format differs between Version 2 and Version 3, with the latter providing
enhanced timestamps (64-bit encoding of the seconds part and nanosecond precision).
┌─────────────────────────────────────────────────────────────┐
│ Version 2 │
├────────┬────────┬───────────────────────────────────────────┤
│Offset │ Length │ Name │
├────────┼────────┼───────────────────────────────────────────┤
│ 0 │ 4 │ timestamp, seconds part (past UNIX epoch) │
│ 4 │ 4 │ timestamp, microseconds part │
│ 8 │ 4 │ number of metrics with data following │
│ 12 │ M │ pmValueSet #0 │
│ 12+M │ N │ pmValueSet #1 │
│ 12+M+N │ ... │ ... │
│ NOP │ X │ pmValueBlock #0 │
│ NOP+X │ Y │ pmValueBlock #1 │
│NOP+X+Y │ ... │ ... │
└────────┴────────┴───────────────────────────────────────────┘
┌─────────────────────────────────────────────────────────────┐
│ Version 3 │
├────────┬────────┬───────────────────────────────────────────┤
│Offset │ Length │ Name │
├────────┼────────┼───────────────────────────────────────────┤
│ 0 │ 8 │ timestamp, seconds part (past UNIX epoch) │
│ 8 │ 4 │ timestamp, nanoseconds part │
│ 12 │ 4 │ number of metrics with data following │
│ 16 │ M │ pmValueSet #0 │
│ 16+M │ N │ pmValueSet #1 │
│ 16+M+N │ ... │ ... │
│ NOP │ X │ pmValueBlock #0 │
│ NOP+X │ Y │ pmValueBlock #1 │
│NOP+X+Y │ ... │ ... │
└────────┴────────┴───────────────────────────────────────────┘
Records with a ``number of metrics'' equal to zero are ``mark records'', and represent
interruptions, missing data, or time discontinuities in logging.
pmValueSet
This subrecord represents the values for one metric at one point in time.
┌───────┬────────┬────────────────────────────────────────────────┐
│Offset │ Length │ Name │
├───────┼────────┼────────────────────────────────────────────────┤
│ 0 │ 4 │ Performance Metrics Identifier (PMID) │
│ 4 │ 4 │ number of values │
│ 8 │ 4 │ value format, PM_VAL_INSITU=0 or PM_VAL_DPTR=1 │
│ 12 │ M │ pmValue #0 │
│ 12+M │ N │ pmValue #1 │
│12+M+N │ ... │ ... │
└───────┴────────┴────────────────────────────────────────────────┘
The metadata describing metrics is found in the .meta file where the entries are not
timestamped, as the metadata is assumed to be unchanging throughout an archive.
pmValue
This subrecord represents one value for one instance of a metric at one point in time. It
is a variant type, depending on the parent pmValueSet's value format field. This allows
small numbers to be encoded compactly, but retain flexibility for larger or variable
length data to be stored later in the pmResult record in a pmValueBlock subrecord.
┌───────┬────────┬────────────────────────────────────────────────────────────────────────┐
│Offset │ Length │ Name │
├───────┼────────┼────────────────────────────────────────────────────────────────────────┤
│ 0 │ 4 │ internal instance identifier (or PM_IN_NULL=-1 for singular metrics) │
│ 4 │ 4 │ value (INSITU) or │
│ │ │ offset in pmResult to our pmValueBlock (DPTR) │
└───────┴────────┴────────────────────────────────────────────────────────────────────────┘
The metadata describing the instance domain for metrics is found in the .meta file. Since
the numeric mappings may change during the lifetime of the logging session, it is
important to match up the timestamp of the measurement record with the corresponding
instance domain record. That is, the instance domain corresponding to a measurement at
time T is the instance domain observation for the metric's instance domain with largest
timestamp T' <= T.
pmValueBlock
Instances of this subrecord are placed at the end of the pmValueSet, after all the pmValue
subrecords. If (and only if) needed, they are padded at the end to the next 32-bit
boundary.
┌───────┬────────┬────────────────────────────────────────────────┐
│Offset │ Length │ Name │
├───────┼────────┼────────────────────────────────────────────────┤
│ 0 │ 1 │ value type (same as pmDesc.type) │
│ 1 │ 3 │ 4 + N, the length of the subrecord │
│ 4 │ N │ bytes that make up the raw value │
│ 4+N │ 0-3 │ padding (not included in the 4+N length field) │
└───────┴────────┴────────────────────────────────────────────────┘
Note that for PM_TYPE_STRING, the length includes an explicit NULL terminator byte. For
PM_TYPE_EVENT, the value byte string is further structured. Refer to PMDAEVENTARRAY(3)
for more information about how arrays of event records are packed inside a pmResult
container.
METADATA FILE (.meta) RECORDS
After the archive label record, the metadata file contains interleaved metric description
records, timestamped instance domain records, timestamped label records (for context,
instance domain and metric labels) and (help) text records. Unlike the data volumes,
these records are not forced to 32-bit alignment.
For Version 2 the file size is limited to 2GiB, due to storage of 32-bit byte offsets
within the temporal index. For Version 3 the file size is limited to 8191PiB, due to
storage of 62-bit byte offsets within the temporal index.
See also libpcp/src/logmeta.c.
Metric Descriptions
Instances of this (pmDesc) record provide the description or metadata for each metric
appearing in the PCP archive. This metadata includes the metric's PMID, data type, data
semantics, instance domain identifier (or PM_INDOM_NULL for singular metrics with only one
value) and a set of (1 or more) names.
┌───────┬────────┬───────────────────────────────────────────────────┐
│Offset │ Length │ Name │
├───────┼────────┼───────────────────────────────────────────────────┤
│ 0 │ 4 │ tag, TYPE_DESC=1 │
│ 4 │ 4 │ PMID │
│ 8 │ 4 │ data type (PM_TYPE_*) │
│ 12 │ 4 │ instance domain identifier │
│ 16 │ 4 │ metric semantics (PM_SEM_*) │
│ 20 │ 4 │ units: bit-packed pmUnits │
│ 4 │ 4 │ number of alternative names for this PMID │
│ 28 │ 4 │ N: number of bytes in this name │
│ 32 │ N │ bytes of the name, no NULL terminator nor padding │
│ 32+N │ 4 │ N2: number of bytes in next name │
│ 36+N │ N2 │ bytes of the name, no NULL terminator nor padding │
│ ... │ ... │ ... │
└───────┴────────┴───────────────────────────────────────────────────┘
Instance Domains
A set-valued metric is defined over an instance domain, which consists of an instance
domain identifier (will have already been mentioned in a prior pmDesc record), a count of
the number of instances and a map that defines the association between internal instance
identifiers (integers) and external instance names (strings).
Because instance domains can change over time, the instance domain also requires a
timestamp, and the same instance domain can occur multiple times within the .meta file.
The timestamps are used to search for the temporally correct instance domain when decoding
pmResult records from the archive data volumes, or answering metadata queries against the
instance domain.
The instance domain format differs markedly between Version 2 and Version 3. Version 3
provides enhanced timestamps (64-bit encoding of the seconds part and nanosecond
precision) and introduces a new ``delta'' instance domain format that encodes differences
between the previous observation of the instance domain and the current state of the
instance domain.
┌──────────────────────────────────────────────────────────────────┐
│ Full Instance Domain - Version 2 │
├─────────┬────────┬───────────────────────────────────────────────┤
│ Offset │ Length │ Name │
├─────────┼────────┼───────────────────────────────────────────────┤
│ 0 │ 4 │ tag, TYPE_INDOM_V2=2 │
│ 4 │ 4 │ timestamp, seconds part (past UNIX epoch) │
│ 8 │ 4 │ timestamp, microseconds part │
│ 12 │ 4 │ instance domain number │
│ 16 │ 4 │ N: number of instances in domain, normally >0 │
│ 20 │ 4 │ first instance number │
│ 24 │ 4 │ second instance number (if appropriate) │
│ ... │ ... │ ... │
│ 20+4*N │ 4 │ first offset into string table (see below) │
│20+4*N+4 │ 4 │ second offset into string table (etc.) │
│ ... │ ... │ ... │
│ 20+8*N │ M │ base of string table, containing │
│ │ │ packed, NULL-terminated instance names │
└─────────┴────────┴───────────────────────────────────────────────┘
┌──────────────────────────────────────────────────────────────────┐
│ Full Instance Domain - Version 3 │
├─────────┬────────┬───────────────────────────────────────────────┤
│ Offset │ Length │ Name │
├─────────┼────────┼───────────────────────────────────────────────┤
│ 0 │ 4 │ tag, TYPE_INDOM=5 │
│ 4 │ 8 │ timestamp, seconds part (past UNIX epoch) │
│ 12 │ 4 │ timestamp, nanoseconds part │
│ 16 │ 4 │ instance domain number │
│ 20 │ 4 │ N: number of instances in domain, normally >0 │
│ 24 │ 4 │ first instance number │
│ 28 │ 4 │ second instance number (if appropriate) │
│ ... │ ... │ ... │
│ 24+4*N │ 4 │ first offset into string table (see below) │
│24+4*N+4 │ 4 │ second offset into string table (etc.) │
│ ... │ ... │ ... │
│ 24+8*N │ M │ base of string table, containing │
│ │ │ packed, NULL-terminated instance names │
└─────────┴────────┴───────────────────────────────────────────────┘
The ``delta'' instance domain record in Version 3 uses the same physical structure as the
``full'' instance domain above with the following differences:
* The tag is TYPE_INDOM_DELTA=6.
* The ``number of instances in domain'' field becomes the sum of the number of instances
added and the number of instances deleted.
* Deleted instances are encoded with the string offset set to -1 and there is no
corresponding string table entry.
* Added instances are encoded exactly the same way.
The ``delta'' instance domain format is used to provide a more compact on-disk encoding
for instance domains that have a large number of instances and are subject to frequent
small changes, e.g. the instance domain of process ids, as exported by pmdaproc(1).
For ``full'' instance domain records the instance domain replace the previous instance
domain: prior records are not searched for instance domain metadata queries after this
timestamp.
Each instance domain in a Version 3 archive must have an initial ``full'' instance domain
record. Subsequent records for the same instance domain can be the `full'' or the
``delta'' variant. Any instance mentioned in the prior observation of an instance domain
that is not mentioned in the ``delta'' instance domain record is assumed to continue to
exist for the current observation of the instance domain.
Labels for Contexts, Instance Domains and Metrics
Instances of this (pmLogLabelSet) record provide sets of label-name:label-value pairs
associated with labels of the context, instance domains and individual performance metrics
- refer to pmLookupLabels(3) for further details.
Any instance domain identifier will have already been mentioned in a prior pmDesc record.
As new labels can appear during an archiving session, these records are timestamped and
must be searched when decoding pmResult records from the archive data volumes. The
pmLogLabelSet format differs between Version 2 and Version 3, with the latter providing
enhanced timestamps (64-bit encoding of the seconds part and nanosecond precision).
┌─────────────────────────────────────────────────────────────────────────────────────────┐
│ Version 2 │
├────────────┬────────┬───────────────────────────────────────────────────────────────────┤
│ Offset │ Length │ Name │
├────────────┼────────┼───────────────────────────────────────────────────────────────────┤
│ 0 │ 4 │ tag, TYPE_LABEL_V2=3 │
│ 4 │ 4 │ timestamp, seconds part (past UNIX epoch) │
│ 8 │ 4 │ timestamp, microseconds part │
│ 12 │ 4 │ label type (PM_LABEL_* type macros.) │
│ 16 │ 4 │ numeric identifier - domain, PMID, etc or PM_IN_NULL=-1 for │
│ │ │ context labels │
│ 20 │ 4 │ N: number of label sets in this record, usually 1 except in the │
│ │ │ case of instances │
│ 24 │ 4 │ offset to the start of the JSONB labels string │
│ 28 │ L1 │ first labelset array entry (see below) │
│ ... │ ... │ ... │
│ 28+L1 │ LN │ N-th labelset array entry (see below) │
│ ... │ ... │ ... │
│28+L1+...LN │ M │ concatenated JSONB strings for all labelsets │
└────────────┴────────┴───────────────────────────────────────────────────────────────────┘
┌─────────────────────────────────────────────────────────────────────────────────────────┐
│ Version 3 │
├────────────┬────────┬───────────────────────────────────────────────────────────────────┤
│ Offset │ Length │ Name │
├────────────┼────────┼───────────────────────────────────────────────────────────────────┤
│ 0 │ 4 │ tag, TYPE_LABEL=7 │
│ 4 │ 8 │ timestamp, seconds part (past UNIX epoch) │
│ 12 │ 4 │ timestamp, nanoseconds part │
│ 16 │ 4 │ label type (PM_LABEL_* type macros.) │
│ 20 │ 4 │ numeric identifier - domain, PMID, etc or PM_IN_NULL=-1 for │
│ │ │ context labels │
│ 24 │ 4 │ N: number of label sets in this record, usually 1 except in the │
│ │ │ case of instances │
│ 28 │ 4 │ offset to the start of the JSONB labels string │
│ 32 │ L1 │ first labelset array entry (see below) │
│ ... │ ... │ ... │
│ 32+L1 │ LN │ N-th labelset array entry (see below) │
│ ... │ ... │ ... │
│32+L1+...LN │ M │ concatenated JSONB strings for all labelsets │
└────────────┴────────┴───────────────────────────────────────────────────────────────────┘
Records of this form replace the existing labels for a given label type: prior records are
not searched for resolving that class of label in measurements after this timestamp.
The individual labelset array entries are variable length, depending on the number of
labels present within that set. These entries contain the instance identifiers (in the
case of type PM_LABEL_INSTANCES labels), lengths and offsets of each label name and value,
and also any flags set for each label.
┌───────┬────────┬───────────────────────────────────────────┐
│Offset │ Length │ Name │
├───────┼────────┼───────────────────────────────────────────┤
│ 0 │ 4 │ instance identifier (or PM_IN_NULL=-1) │
│ 4 │ 4 │ length of JSONB label string │
│ 8 │ 4 │ N: number of labels in this labelset │
│ 12 │ 2 │ first label name offset │
│ 14 │ 1 │ first label name length │
│ 15 │ 1 │ first label flags (e.g. optionality) │
│ 16 │ 2 │ first label value offset │
│ 18 │ 2 │ first label value length │
│ 20 │ 2 │ second label name offset (if appropriate) │
│ ... │ ... │ ... │
└───────┴────────┴───────────────────────────────────────────┘
Help Text
This (pmLogText) record stores help text associated with a metric or an instance domain -
as provided by pmLookupText(3) and pmLookupInDomText(3).
The metric identifier and instance domain identifier will have already been mentioned in a
prior pmDesc record.
┌───────┬────────┬──────────────────────────────────────────────┐
│Offset │ Length │ Name │
├───────┼────────┼──────────────────────────────────────────────┤
│ 0 │ 4 │ tag, TYPE_TEXT=4 │
│ 4 │ 4 │ text and identifier type (PM_TEXT_* macros.) │
│ 8 │ 4 │ numeric identifier - PMID or instance domain │
│ 12 │ M │ help text string, arbitrary text │
└───────┴────────┴──────────────────────────────────────────────┘
INDEX FILE (.index) RECORDS
After the archive label record, the temporal index file contains a plainly concatenated,
unframed group of tuples, which relate timestamps to the byte offsets in the volume and
.meta files. These records are fixed size, fixed format, and are not enclosed in the
standard length/payload/length wrapper: they take up the entire remainder of the .index
file after the archive label record.
The temporal index file provides a rapid way of seeking to a particular point of time
within an archive for both the performance metric values and the associated metadata.
See also libpcp/src/logutil.c.
The index format differs between Version 2 and Version 3, with the latter providing
enhanced timestamps (64-bit encoding of the seconds part and nanosecond precision) and
64-bit byte offsets.
┌────────────────────────────────────────────────────────────┐
│ Version 2 │
├───────┬────────┬───────────────────────────────────────────┤
│Offset │ Length │ Name │
├───────┼────────┼───────────────────────────────────────────┤
│ 0 │ 4 │ timestamp, seconds part (past UNIX epoch) │
│ 4 │ 4 │ timestamp, microseconds part │
│ 8 │ 4 │ archive volume number (0...N) │
│ 12 │ 4 │ byte offset in .meta file │
│ 16 │ 4 │ byte offset in archive volume file │
└───────┴────────┴───────────────────────────────────────────┘
┌────────────────────────────────────────────────────────────┐
│ Version 3 │
├───────┬────────┬───────────────────────────────────────────┤
│Offset │ Length │ Name │
├───────┼────────┼───────────────────────────────────────────┤
│ 0 │ 8 │ timestamp, seconds part (past UNIX epoch) │
│ 8 │ 4 │ timestamp, nanoseconds part │
│ 12 │ 4 │ archive volume number (0...N) │
│ 16 │ 8 │ byte offset in .meta file │
│ 24 │ 8 │ byte offset in archive volume file │
└───────┴────────┴───────────────────────────────────────────┘
Since the temporal index is optional, and exists only to speed up time-based random access
to metrics and their metadata, the index records are emitted only intermittently. An
archive reader program should not presume any particular rate of data flow into the index.
However, common events that may trigger a new temporal index record include changes in
instance domains, switching over to a new archive volume, and starting or stopping
logging. One reliable invariant however is that, for each index entry, there are to be no
meta or archive volume records with a timestamp after that in the index, but physically
before the associated byte offset in the index.
FILES
Several PCP tools create archives in standard locations:
$HOME/.pcp/pmlogger
default location for the interactive chart recording mode in pmchart(1)
$PCP_LOG_DIR/pmlogger
default location for pmlogger_daily(1) and pmlogger_check(1) scripts
SEE ALSO
mkaf(1), PCPIntro(1), pmafm(1), pmchart(1), pmdaproc(1), pmdumplog(1), pmlogger(1),
pmlogger_check(1), pmlogger_daily(1), pmlogreduce(1), pmlogrewrite(1), pmlogsummary(1),
LOGIMPORT(3), PMAPI(3), pmLookupDesc(3), pmLookupInDom(3), pmLookupInDomText(3),
pmLookupLabels(3), pmLookupName(3), pmLookupText(3), pcp.conf(5) and pcp.env(5).