Compatibility layer for clickhouse-operator metric exporter

CREATE VIEW system.operator_compatible_metrics
(
    `name` String,
    `value` Float64,
    `help` String,
    `labels` Map(String, String),
    `type` String
) AS
SELECT
    concat('chi_clickhouse_event_', event) AS name,
    CAST(value, 'Float64') AS value,
    description AS help,
    map('hostname', hostName()) AS labels,
    'counter' AS type
FROM system.events
UNION ALL
SELECT
    concat('chi_clickhouse_metric_', metric) AS name,
    CAST(value, 'Float64') AS value,
    description AS help,
    map('hostname', hostName()) AS labels,
    'gauge' AS type
FROM system.metrics
UNION ALL
SELECT
    concat('chi_clickhouse_metric_', metric) AS name,
    value,
    '' AS help,
    map('hostname', hostName()) AS labels,
    'gauge' AS type
FROM system.asynchronous_metrics
UNION ALL
SELECT
    'chi_clickhouse_metric_MemoryDictionaryBytesAllocated' AS name,
    CAST(sum(bytes_allocated), 'Float64') AS value,
    'Memory size allocated for dictionaries' AS help,
    map('hostname', hostName()) AS labels,
    'gauge' AS type
FROM system.dictionaries
UNION ALL
SELECT
    'chi_clickhouse_metric_LongestRunningQuery' AS name,
    CAST(max(elapsed), 'Float64') AS value,
    'Longest running query time' AS help,
    map('hostname', hostName()) AS labels,
    'gauge' AS type
FROM system.processes
UNION ALL
WITH
    ['chi_clickhouse_table_partitions', 'chi_clickhouse_table_parts', 'chi_clickhouse_table_parts_bytes', 'chi_clickhouse_table_parts_bytes_uncompressed', 'chi_clickhouse_table_parts_rows', 'chi_clickhouse_metric_DiskDataBytes', 'chi_clickhouse_metric_MemoryPrimaryKeyBytesAllocated'] AS names,
    [uniq(partition), count(), sum(bytes), sum(data_uncompressed_bytes), sum(rows), sum(bytes_on_disk), sum(primary_key_bytes_in_memory_allocated)] AS values,
    arrayJoin(arrayZip(names, values)) AS tpl
SELECT
    tpl.1 AS name,
    CAST(tpl.2, 'Float64') AS value,
    '' AS help,
    map('database', database, 'table', table, 'active', toString(active), 'hostname', hostName()) AS labels,
    'gauge' AS type
FROM system.parts
GROUP BY
    active,
    database,
    table
UNION ALL
WITH
    ['chi_clickhouse_table_mutations', 'chi_clickhouse_table_mutations_parts_to_do'] AS names,
    [CAST(count(), 'Float64'), CAST(sum(parts_to_do), 'Float64')] AS values,
    arrayJoin(arrayZip(names, values)) AS tpl
SELECT
    tpl.1 AS name,
    tpl.2 AS value,
    '' AS help,
    map('database', database, 'table', table, 'hostname', hostName()) AS labels,
    'gauge' AS type
FROM system.mutations
WHERE is_done = 0
GROUP BY
    database,
    table
UNION ALL
WITH if(coalesce(reason, 'unknown') = '', 'detached_by_user', coalesce(reason, 'unknown')) AS detach_reason
SELECT
    'chi_clickhouse_metric_DetachedParts' AS name,
    CAST(count(), 'Float64') AS value,
    '' AS help,
    map('database', database, 'table', table, 'disk', disk, 'hostname', hostName()) AS labels,
    'gauge' AS type
FROM system.detached_parts
GROUP BY
    database,
    table,
    disk,
    reason
ORDER BY name ASC

nano /etc/clickhouse-server/config.d/operator_metrics.xml
<clickhouse>
    <http_handlers>
        <rule>
            <url>/metrics</url>
            <methods>POST,GET</methods>
            <handler>
                <type>predefined_query_handler</type>
                <query>SELECT * FROM system.operator_compatible_metrics FORMAT Prometheus</query>
                <content_type>text/plain; charset=utf-8</content_type>
            </handler>
        </rule>
        <defaults/>
        <rule>
            <url>/</url>
            <methods>POST,GET</methods>
            <headers><pragma>no-cache</pragma></headers>
            <handler>
                <type>dynamic_query_handler</type>
                <query_param_name>query</query_param_name>
            </handler>
        </rule>
    </http_handlers>    
</clickhouse>

curl http://localhost:8123/metrics
# HELP chi_clickhouse_metric_Query Number of executing queries
# TYPE chi_clickhouse_metric_Query gauge
chi_clickhouse_metric_Query{hostname="LAPTOP"} 1

# HELP chi_clickhouse_metric_Merge Number of executing background merges
# TYPE chi_clickhouse_metric_Merge gauge
chi_clickhouse_metric_Merge{hostname="LAPTOP"} 0

# HELP chi_clickhouse_metric_PartMutation Number of mutations (ALTER DELETE/UPDATE)
# TYPE chi_clickhouse_metric_PartMutation gauge
chi_clickhouse_metric_PartMutation{hostname="LAPTOP"} 0