Multi-File Disk Stores
Persistent events on channels and queues are stored in a file-based store that uses one or more files for each channel and queue on that realm. See the sections
Channel Attributes and
Queue Attributes for related information about the channel/queue type
Persistent.
If you set the value of the storage property Events Per Spindle for any channel or queue to 0, the store will persist all events for that channel or queue in a single disk file. If you set this storage property to a value greater than 0, the events for the channel or queue will be persisted in multiple files, also known as spindles. The maximum number of events that can be stored in a spindle is given by Events Per Spindle. When the capacity of a spindle is reached, a new spindle will be created. Each spindle has the file type mem.
See the description of
Events Per Spindle in the section
Storage Properties of Channels and Queues for related information.
Note:
It is possible that events in a spindle get flagged as "purged" (for example, if an event's time-to-live setting has been reached and the event is therefore no longer required). This can happen while there is still capacity to append new events at the end of the spindle, or even after the spindle capacity has been reached. However, space for purged events in a spindle is never freed up for storing new events; new events are only ever appended to the end of the most recent, unfilled spindle. Thus, a spindle is considered full, i.e. its capacity is reached, when the total number of purged and non-purged events in the spindle is equal to Events Per Spindle.
Having multiple spindles allows you to optimize the use of disk space by being able to delete individual spindles if they are no longer required. An individual spindle will be deleted only if BOTH of the following conditions are met:
When the spindle is full, i.e. when the total number of purged and non-purged events defined by the
Events Per Spindle property are stored in it. Before the spindle gets full it cannot be deleted and a new spindle will not be created.
When all events from the spindle have been flagged as "purged". If there are non-purged events in the spindle, it will not be deleted or resized.
Note:
For stores of type Mixed, when only non-persistent events are used, new spindles will still be created; however, they will not contain the original events but instead just some metadata for each event.