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1 Foreach functions

Overview

Foreach functions are used in aggregate calculations to return one aggregate value for each item that is selected by the used item filter.

For example, the avg_foreach function will return the average value from the history of each selected item, during the time interval that is specified.

The item filter is part of the syntax used by foreach functions. The use of wildcards is supported in the item filter, thus the required items can be selected quite flexibly.

Supported functions

Function Description
avg_foreach Returns the average value for each item.
bucket_rate_foreach Returns pairs (bucket upper bound, rate value) suitable for use in the histogram_quantile() function, where "bucket upper bound" is the value of item key parameter defined by the <parameter number> parameter.
count_foreach Returns the number of values for each item.
exists_foreach Returns the number of currently enabled items.
last_foreach Returns the last value for each item.
max_foreach Returns the maximum value for each item.
min_foreach Returns the minimum value for each item.
sum_foreach Returns the sum of values for each item.

Function syntax

Foreach functions support two common parameters: item filter (see details below) and time period:

foreach_function(item filter,time period)

For example:

avg_foreach(/*/mysql.qps?[group="MySQL Servers"],5m)

will return the five-minute average of each 'mysql.qps' item in the MySQL server group.

Note that some functions support additional parameters.

Item filter syntax

The item filter:

/host/key[parameters]?[conditions]

consists of four parts, where:

  • host - host name
  • key - item key (without parameters)
  • parameters - item key parameters
  • conditions - host group and/or item tag based conditions (as expression)

Spaces are allowed only inside the conditions expression.

Wildcard usage

  • Wildcard can be used to replace the host name, item key or an individual item key parameter.
  • Either the host or item key must be specified without wildcard. So /host/* and /*/key are valid filters, but /*/* is invalid.
  • Wildcard cannot be used for a part of host name, item key, item key parameter.
  • Wildcard does not match more than a single item key parameter. So a wildcard must be specified for each parameter in separation (i.e. key[abc,*,*]).

Conditions expression

The conditions expression supports:

  • operands:
    • group - host group
    • tag - item tag
    • "<text>" - string constant, with the \ escape character to escape " and \
  • case-sensitive string comparison operators: =, <>
  • logical operators: and, or, not
  • grouping with parentheses: ( )

Quotation of string constants is mandatory. Only case-sensitive full string comparison is supported.

Examples

A complex filter may be used, referencing the item key, host group and tags, as illustrated by the examples:

Syntax example Description
/host/key[abc,*] Matches similar items on this host.
/*/key Matches the same item of any host.
/*/key?[group="ABC" and tag="tagname:value"] Matches the same item of any host from the ABC group having 'tagname:value' tags.
/*/key[a,*,c]?[(group="ABC" and tag="Tag1") or (group="DEF" and (tag="Tag2" or tag="Tag3:value"))] Matches similar items of any host from the ABC or DEF group with the respective tags.

All referenced items must exist and collect data. Only enabled items on enabled hosts are included in the calculations.

If the item key of a referenced item is changed, the filter must be updated manually.

Specifying a parent host group includes the parent group and all nested host groups with their items.

Time period

The second parameter allows to specify the time period for aggregation. The time period can only be expressed as time, the amount of values (prefixed with #) is not supported.

Supported unit symbols can be used in this parameter for convenience, for example '5m' (five minutes) instead of '300s' (300 seconds) or '1d' (one day) instead of '86400' (86400 seconds).

Time period is ignored by the server if passed with the last_foreach function and can thus be omitted:

last_foreach(/*/key?[group="host group"])

Time period is not supported with the exists_foreach function.

Additional parameters

A third optional parameter is supported by the bucket_rate_foreach function:

bucket_rate_foreach(item filter,time period,<parameter number>)

where <parameter number> is the position of the "bucket" value in the item key. For example, if the "bucket" value in myItem[aaa,0.2] is '0.2', then its position is 2.

The default value of <parameter number> is '1'.

See aggregate calculations for more details and examples on using foreach functions.