POSTGRES_TOPOLOGY_SETTINGS

POSTGRES_TOPOLOGY_SETTINGS Dynamic Config

Dynamic config that controls topology settings of service's PostgreSQL components.

Dictionary keys can be either the value of name_alias static configuration option of the PostgreSQL component (not database name!) or __default__. The latter configuration is applied for every non-matching PostgreSQL component of the service.

Take note that a matching object replaces all static topology settings rather than merging individual fields! In particular, omitting rtt_threshold_ms from a matching object uses the 20ms default, even if static rtt_threshold has a different value.

Schema:

# yaml
default: {}
description: |
    Dynamic config that controls topology settings of service's PostgreSQL
    components.
 
    Dictionary keys can be either the value of `name_alias` static configuration option of the PostgreSQL component
    (**not database name!**) or `__default__`. The latter configuration is applied for every non-matching
    PostgreSQL component of the service.
 
    Take note that a matching object replaces all static topology settings rather than merging individual fields!
    In particular, omitting `rtt_threshold_ms` from a matching object uses the 20ms default, even if static
    `rtt_threshold` has a different value.
schema:
    type: object
    example: |
        {
            // settings for a specific component
            "postgresql-orders": {
                "max_replication_lag_ms": 0,
                "rtt_threshold_ms": 15,
                "disabled_replicas": ["sas-01.db.yandex.net", "vla-02.db.yandex.net"]
            },
            // settings for all other components
            "__default__": {
                "max_replication_lag_ms": 60000
            }
        }
    additionalProperties:
        $ref: "#/definitions/TopologySettings"
    definitions:
        TopologySettings:
            type: object
            additionalProperties: false
            properties:
                max_replication_lag_ms:
                    type: integer
                    minimum: 0
                    description: |
                        Replication lag limit in milliseconds for usable replicas. If a replica's lag exceeds this
                        value, it stops receiving new requests.
                rtt_threshold_ms:
                    type: integer
                    minimum: 0
                    maximum: 60000
                    default: 20
                    description: |
                        Maximum EWMA RTT difference in milliseconds from the fastest alive host. It is used to prefer
                        hosts when no selection strategy is specified or when `kRoundRobin` is requested. Values must
                        not exceed one minute. Zero is valid and prefers only hosts tied for the lowest RTT. Slower
                        hosts remain available and are used when no eligible host has a known RTT. The same EWMA RTT
                        estimate is used by nearest selection and RTT metrics. RTT preference is enabled by default
                        and controlled by the `POSTGRES_RTT_THRESHOLD_ENABLED` dynamic config.
                disabled_replicas:
                    type: array
                    x-taxi-cpp-type: std::unordered_set
                    description: List of force disabled replicas (FQDN).
                    items:
                        type: string
            required:
              - max_replication_lag_ms

Example:

{
    // settings for a specific component
    "postgresql-orders": {
        "max_replication_lag_ms": 0,
        "rtt_threshold_ms": 15,
        "disabled_replicas": ["sas-01.db.yandex.net", "vla-02.db.yandex.net"]
    },
    // settings for all other components
    "__default__": {
        "max_replication_lag_ms": 60000
    }
}

For a full list of dynamic configs see Dynamic config schemas list