Configure the internal queue

Heartbeat uses an internal queue to store events before publishing them. The queue is responsible for buffering and combining events into batches that can be consumed by the outputs. The outputs will use bulk operations to send a batch of events in one transaction.

You can configure the type and behavior of the internal queue by setting options in the queue section of the heartbeat.yml config file. Only one queue type can be configured.

This sample configuration sets the memory queue to buffer up to 4096 events:

queue.mem:
  events: 4096

The memory queue keeps all events in memory.

If no flush interval and no number of events to flush is configured, all events published to this queue will be directly consumed by the outputs. To enforce spooling in the queue, set the flush.min_events and flush.timeout options.

By default flush.min.events is set to 2048 and flush.timeout is set to 1s.

The output’s bulk_max_size setting limits the number of events being processed at once.

The memory queue waits for the output to acknowledge or drop events. If the queue is full, no new events can be inserted into the memory queue. Only after the signal from the output will the queue free up space for more events to be accepted.

This sample configuration forwards events to the output if 512 events are available or the oldest available event has been waiting for 5s in the queue:

queue.mem:
  events: 4096
  flush.min_events: 512
  flush.timeout: 5s

You can specify the following options in the queue.mem section of the heartbeat.yml config file:

Number of events the queue can store.

The default value is 4096 events.

Minimum number of events required for publishing. If this value is set to 0, the output can start publishing events without additional waiting times. Otherwise the output has to wait for more events to become available.

The default value is 2048.

Maximum wait time for flush.min_events to be fulfilled. If set to 0s, events will be immediately available for consumption.

The default value is 1s.

The file spool queue stores all events in an on disk ring buffer. The spool has a write buffer, which new events are written to. Events written to the spool are forwarded to the outputs, only after the write buffer has been flushed successfully.

The spool waits for the output to acknowledge or drop events. If the spool is full, no new events can be inserted. The spool will block. Space is freed only after a signal from the output has been received.

On disk, the spool divides a file into pages. The file.page_size setting configures the file’s page size at file creation time. The optimal page size depends on the effective block size, used by the underlying file system.

This sample configuration enables the spool with all default settings (See Configuration options for defaults) and the default file path:

queue.spool: ~

This sample configuration creates a spool of 512MiB, with 16KiB pages. The write buffer is flushed if 10MiB of contents, or 1024 events have been written. If the oldest available event has been waiting for 5s in the write buffer, the buffer will be flushed as well:

queue.spool:
  file:
    path: "${path.data}/spool.dat"
    size: 512MiB
    page_size: 16KiB
  write:
    buffer_size: 10MiB
    flush.timeout: 5s
    flush.events: 1024

You can specify the following options in the queue.spool section of the heartbeat.yml config file:

The spool file path. The file is created on startup, if it does not exist.

The default value is "${path.data}/spool.dat".

The file permissions. The permissions are applied when the file is created. In case the file already exists, the file permissions are compared with file.permissions. The spool file is not opened if the actual file permissions are more permissive then configured.

The default value is 0600.

Spool file size.

The default value is 100 MiB.

The file’s page size.

The spool file is split into pages of page_size. All I/O operations operate on complete pages.

The default value is 4096 (4KiB).

If prealloc is set to true, truncate is used to reserve the space up to file.size. This setting is only used when the file is created.

The file will dynamically grow, if prealloc is set to false. The spool blocks, if prealloc is false and the system is out of disk space.

The default value is true.

The write buffer size. The write buffer is flushed, once the buffer size is exceeded.

Very big events are allowed to be bigger then the configured buffer size. But the write buffer will be flushed right after the event has been serialized.

The default value is 1MiB.

The event encoding used for serialized events. Valid values are json and cbor.

The default value is cbor.

Maximum wait time of the oldest event in the write buffer. If set to 0, the write buffer will only be flushed once write.flush.events or write.buffer_size is fulfilled.

The default value is 1s.

Number of buffered events. The write buffer is flushed once the limit is reached.

The default value is 16384.

The spool reader tries to read up to the output’s bulk_max_size events at once.

If read.flush.timeout is set to 0s, all available events are forwarded immediately to the output.

If read.flush.timeout is set to a value bigger then 0s, the spool will wait for more events to be flushed. Events are forwarded to the output if bulk_max_size events have been read or the oldest read event has been waiting for the configured duration.

The default value is 0s.