Object configuration (part 1)

These Liberator configuration items define how Liberator deals with objects.

A Liberator object is a piece of data that Liberator manages on behalf of client applications; for example, a financial instrument such as a DataSource record containing a currency pair. Liberator object types include all the DataSource data types, and data types that are additional to StreamLink, such as the Chat type.

More object-related configuration can be found in Object configuration (part 2), Throttling and Throttling configuration.

Contents:

add-object
Object types and object numbers
Directories

add-object

add-object adds an object name to Liberator and defines the object’s characteristics. The object is local to Liberator, which means it’s created in Liberator’s cache. It isn’t updated from any DataSource peers (Integration Adapters or Transformers) unless a) it’s a broadcast object that originates from a peer, or b) it’s a directory object (see Directories, below, and DataSource > Directories), in which case the data for the subjects subscribed to under that directory is supplied from the relevant peer(s).

Syntax

add-object
   discard-timeout            [integer]
   disable-generic-throttling [boolean]
   flags                      [integer]
   name                       [string]
   no-batching                [boolean]
   only-changed-fields        [boolean]
   purge-age                  [integer]
   purge-period               [integer]
   purge-time                 [integer]
   record-type3-history-size  [integer]
   throttle-times             [array of floats]
   timestamp-field            [string]
   type                       [integer/string]
end-object

Options

discard-timeout

Type: integer | Default: see description below

The time in seconds for which the Liberator holds on to an object in the directory after the last user stops viewing it. After this time, the object is deleted from the Liberator’s cache and Liberator sends a discard instruction to the supplying DataSource peer to cancel the subscription to the object.

This option overrides any settings of the discard-timeout for the data service that fetches data for the object (see the discard-timeout option of add-data-service). It also overrides the setting of the global item active-discard-timeout for this directory object.

The value defaults to the discard-timeout for the data service that fetches data for the object.

disable-generic-throttling

Type: boolean | Default: null

Updates from generic objects are throttled by default from Liberator 7.1.24. To reverse this change in behaviour for a specific namespace, set the option disable-generic-throttling to true on an object of type directory. Alternatively, to reverse this change in behaviour for all namespaces, set the global configuration item object-disable-generic-throttling to true.

To disable throttling for all objects in a specific namespace, see the option throttle-times. To disable throttling for all objects in all namespaces, set the global option object-throttle-off to true.

flags

Type: integer | Default: 32

Flags specifying additional characteristics for the object when it is created.

Valid values are:

32 - Create the object’s parent directories as well as the target object.

For example, if name is /A/B/C, create the parent directories A and B as well as C. This is the default flags setting and it can’t be disabled.
128 - Create empty data for the object type. For example, if name is /A and type is record, an empty record with subject /A is created.

To specify both flags, use the value 160 (=32+128).

name

Type: string | Default: null

The name of the object. For example, /B/record1

no-batching

Type: boolean | Default: FALSE

When TRUE, updates to objects that match the name option are not batched.

Normally, when an update to a matching object is received, the update message is added to the queue of batched messages, and all messages in the queue are immediately sent to the client. The no-batching option overrides the burst-min and burst-max configuration settings.

Set this item to TRUE for objects that define the subjects of trade messages, since trade messages should be propagated to clients with minimum possible latency and so must never be batched. For example, if the name option of add-object is set to /TRADE, (thus specifying the subject that identifies trade messages), updates to objects that start with /TRADE/ are immediately sent to the client.

only-changed-fields

Type: boolean | Default: FALSE

This option applies only to objects of type record. It can be defined directly on these objects or inherited from the definition of an object of type directory.

This option takes a boolean value:

FALSE (default): client updates contain all updated fields
TRUE: client updates contain only updated fields that have changed in value

You only need to consider setting this option if the Integration Adapter that supplies updates for the objects of interest doesn’t itself transmit just the changed fields. Normally you’d implement Adapters so that they only transmit update information about object fields that have changed, so you wouldn’t need to set only-changed-fields.

Where there are many fields that are infrequently updated, the size of the messages transferred to clients is reduced. However, this feature might require increased server resources and might not be suitable when the majority of fields are frequently updated.

Example 1. add-object for a record

This setting applies to a single record, whose subject is /B/Record1:

add-object
   name                /B/Record1
   type                record
   only-changed-fields TRUE
end-object

Example 2. add-object for a directory

This setting applies to all the records under a single directory called /Dir1:

add-object
   name                /Dir1
   type                directory
   only-changed-fields TRUE
end-object

purge-age

Type: integer | Default: 0

This option applies only to objects of type directory.

How old in minutes objects in the directory need to be before they can be removed from Liberator’s cache. Every purge-period minutes past purge-time, Liberator checks its cache to see which of the directory’s objects can be deleted.

When purge-age is not zero, objects in the directory that have not been updated for purge-period x purge-age minutes are purged (provided no clients are subscribed to them).

When purge-age is zero, all objects in the directory that have no clients subscribed to them are purged, regardless of when they were last updated.

For more about purging directories, see How can I… Control when Liberator purges its object cache.

purge-period

Type: integer | Default: 1440

This option applies only to objects of type directory.

How often in minutes, relative to purge-time, objects in the directory are removed from Liberator’s cache. Every purge-period minutes past purge-time, Liberator checks its cache and deletes any objects in the directory that are older than purge-age and also have no clients subscribed to them.

For more about purging directories, see How can I… Control when Liberator purges its object cache.

purge-time

Type: integer | Default: -1

This option applies only to objects of type directory.

The time when the Liberator is to start purging the objects in the directory by deleting them from its cache. This time is the number of minutes after midnight (local time) on the day the Liberator was started, or if the time’s greater than or equal to 1440 (24 hours), it’s the number of minutes past midnight on a Sunday.

Set purge-time to -1 to never purge the directory on a timed basis, so purge-age and purge-period are ignored.

At purge-time, and subsequently every purge-period minutes past purge-time, Liberator checks its cache and deletes any objects in the directory that are older than purge-age and have no clients subscribed to them.

Use this option in conjunction with purge-period and optionally purge-age, to purge directories at regular intervals. For more about this, see How can I… Control when Liberator purges its object cache.

record-type3-history-size

Type: integer | Default: value of record-type3-history-size

This option applies only to objects of type record containing type 3 data.

This option only applies to record objects containing type 3 data (the history of updates to the record).

Maximum number of type 3 data updates to keep for this object / object hierarchy.

This option overrides (for this object or object hierarchy only) the setting of record-type3-history-size.

throttle-times

Type: array of floats and strings | Default: value of object-throttle-times

This option applies only to objects of type record and generic. It can be defined directly on these objects or inherited from the definition of an object of type directory.

This option overrides the value of global item object-throttle-times.

This configuration item is overridden by add-data-service::throttle-time (Liberator 8), and add-provided-data-service::throttle-time (DataSource 8).

A space-separated array of throttle times (seconds), followed by an optional "stopped" or "paused":

throttle-times time ... [stopped|paused]

…where time is a floating point number or 0.

Specifying multiple times in the array allows client applications to choose the throttle time most suited to their network bandwidth and use case. This is called 'levelling', and the initial level for clients is set by the global item object-throttle-default-level.

Updates from generic objects are throttled from Liberator 7.1.24. Generic objects do not support 'levelling', and throttled updates from generic objects only use the first value in the throttle-times array.

To disable update throttling for this object, set throttle-times to 0. To disable throttling for all subjects, see object-throttle-off.

timestamp-field

Type: string | Default: null

The name of a field into which Liberator adds a timestamp to this object for the purposes of latency measurement. The timestamp allows a client application to calculate the time taken for the record represented by the object to be transmitted to it from this Liberator.

Liberator only adds the timestamp-field, and the timestamp within it, if the object doesn’t already contain a field of that name.

This timestamping facility is independent of the latency chain timestamps, and it isn’t controlled by the setting of the latency-chain-enable configuration item.

This option overrides the global timestamp-field configuration item for this object only.

For information on timestamp precision, see the documentation for the global timestamp-field configuration item.

type

Type: string or integer | Default: null

The object type, as either the object type name or the object type number.

For the list of valid values, see Object types and object numbers below.

Examples:

type record
type 22

Object types and object numbers

Here’s the list of valid object type names, and their corresponding object numbers, that can be specified in the type option of add-object:

Object type name Object type number Description

Object type name	Object type number	Description
chat	27	Chat object
container	28	Container object
directory	20	Directory object
generic	31	Generic object
json^†	32^‡	JSON data
news	23	News headline object
page	21	Page object
permission	30	Permission object
record	22	Record object
story	24	News story object
trade	Alias of `generic`

chat

Chat object

container

Container object

Directories

Use add-object to configure a directory with specific characteristics. For example, to create a directory called /TRADE, define an add-object entry with the name option set to /TRADE and the type option set to directory, and with the other options set as required. Then define a data service with an include-pattern of ^/TRADE (see add-data-service). When Liberator users subscribe to /TRADE they’ll receive objects, under the directory /TRADE, that a DataSource peer configured for the data service has sent to the Liberator, such as records with the subjects /TRADE/ABC, /TRADE/DEF, and so on.

If an object is defined as a directory, all objects that are subsequently subscribed to under that directory inherit the configuration options that were defined in the add-object for the directory.

See also:

Reference: Object configuration (part 2)
How can I… Control when Liberator purges its object cache.
DataSource > Directories