setup_hooks ¶

Type: classy_lib:mfargs/0

A callback that classy executes during startup. It allows business applications to set up other hooks using a more type-safe API.

table_dir ¶

Type: file:filename()

Default: "."

Directory where persistent data is stored. It should be writable.

rpc_timeout ¶

Type: timeout()

Default: 5000

Unit: ms

Default timeout for remote procedure calls.

hook_timeout ¶

Type: timeout()

Default: 30_000

Unit: ms

Maximum run time for any hook.

rand_id_bytes ¶

Type: pos_integer()

Default: 16

Number of bytes used in random identifiers, such as site IDs and cluster IDs.

WARNING: this value should be sufficiently large to account for the birthday problem. Note that new cluster IDs are created every time a node leaves a cluster, so the number of unique random IDs is not limited to the number of sites.

boot_diagnostic_interval ¶

Type: pos_integer()

Default: 15_000

Unit: ms

classy_boot module can print boot state of the node to help diagnose problems. This parameter specifies how often the diagnostics are printed.

NOTE: the message is suppressed when the node is fully booted.

sync_timeout ¶

Type: non_neg_integer()

Default: 1000

Unit: ms

Maximum interval of time that can pass between the membership CRDT server receiving an update and the moment it propagates it to the peers.

n_sites ¶

Type: non_neg_integer()

Default: 1

Minimum number of known peers necessary to advance the run level from single to cluster.

to_cluster_sets ¶

Type: [classy:node_set_name()]

Default: []

List of node set names used to additionally restrict when the node is considered joined to a cluster. Sets from the lists are combined using set intersection operation.

quorum_sets ¶

Type: [classy:node_set_name()]

Default: []

List of node set names used to additionally restrict when the node is considered having a quorum. Sets from the lists are combined using set intersection operation.

quorum ¶

Type: non_neg_integer() | auto

Default: 1

Minimum number of known peers necessary to make quorum decisions and to advance the run level from cluster to quorum.

If set to auto, then the value is calculated as majority n_sites.

vote_retry_interval ¶

Type: pos_integer()

Default: 5000

Unit: ms

2PC coordinator re-sends outcome of a transaction to the participants at this interval.

max_site_downtime ¶

Type: pos_integer() | infinity

Default: infinity

Unit: s.

Automatically kick sites that have been down longer than this value from the cluster.

Note: to prevent network-isolated nodes from kicking their peers, quorum among the running nodes is required to perform the act.

cleanup_check_interval ¶

Type: pos_integer()

Default: 5_000

Unit: ms.

Autoclean check interval.

forget_after ¶

Type: pos_integer()

Default: 1w

Unit: s

Forget information about inactive (kicked) sites after this period of time.

Note: cleanup procedure may lead to the following situation:

1. Site A goes down
2. Site B kicks A
3. Information about event 2 propagates throughout the cluster.
4. Cleanup. All active peers delete data about A.
5. A goes back up

Since at step 4 we removed the data about event 2, A will reappear in the cluster.

So forget_after should be set to a fairly large value to make sure it doesn’t cover nodes that can go back online.

discovery_interval ¶

Type: pos_integer()

Default: 5_000

Unit: ms.

Peer discovery retry interval.

discovery_strategy ¶

Type: classy_discovery_strategy:t/0

Peer discovery method, See Autocluster.

discovery_complete_sets ¶

Type: [classy:node_set_name()]

Default: []

Consider cluster discovery complete when intersection of the site sets specified by this parameter, with the local site subtracted, contains at least one item.