Clickhouse as time-series storage
There are more than one ways to use CH as a time series database. My personal preference is to use one string array for metric names and one Float64 array for metric values.
This is a sample time series table:
CREATE TABLE ts1(
entity String,
ts UInt64, -- timestamp, milliseconds from January 1 1970
m Array(String), -- names of the metrics
v Array(Float32), -- values of the metrics
d Date MATERIALIZED toDate(round(ts/1000)), -- auto generate date from ts column
dt DateTime MATERIALIZED toDateTime(round(ts/1000)) -- auto generate date time from ts column
) ENGINE = MergeTree(d, entity, 8192)
Here we are loading two metrics (load, temperature) for an entity(cpu):
INSERT INTO ts1(entity, ts, m, v)
VALUES ('cpu', 1509232010254, ['load','temp'], [0.85, 68])
And querying cpu load:
SELECT
entity,
dt,
ts,
v[indexOf(m, 'load')] AS load
FROM ts1
WHERE entity = 'cpu'
┌─entity─┬──────────────────dt─┬────────────ts─┬─load─┐
│ cpu │ 2017-10-28 23:06:50 │ 1509232010254 │ 0.85 │
└────────┴─────────────────────┴───────────────┴──────┘
Get data as array of tuples:
SELECT
entity,
dt,
ts,
arrayMap((mm, vv) -> (mm, vv), m, v) AS metrics
FROM ts1
┌─entity─┬──────────────────dt─┬────────────ts─┬─metrics─────────────────────┐
│ cpu │ 2017-10-28 23:06:50 │ 1509232010254 │ [('load',0.85),('temp',68)] │
└────────┴─────────────────────┴───────────────┴─────────────────────────────┘
Get data as rows of tuples:
SELECT
entity,
dt,
ts,
arrayJoin(arrayMap((mm, vv) -> (mm, vv), m, v)) AS metric
FROM ts1
┌─entity─┬──────────────────dt─┬────────────ts─┬─metric────────┐
│ cpu │ 2017-10-28 23:06:50 │ 1509232010254 │ ('load',0.85) │
│ cpu │ 2017-10-28 23:06:50 │ 1509232010254 │ ('temp',68) │
└────────┴─────────────────────┴───────────────┴───────────────┘
Get rows with the metric you want:
SELECT
entity,
dt,
ts,
arrayJoin(arrayMap((mm, vv) -> (mm, vv), m, v)) AS metrics
FROM ts1
WHERE metrics.1 = 'load'
┌─entity─┬──────────────────dt─┬────────────ts─┬─metrics───────┐
│ cpu │ 2017-10-28 23:06:50 │ 1509232010254 │ ('load',0.85) │
└────────┴─────────────────────┴───────────────┴───────────────┘
Get metric names and values as columns:
SELECT
entity,
dt,
ts,
arrayJoin(arrayMap((mm, vv) -> (mm, vv), m, v)) AS metric,
metric.1 AS metric_name,
metric.2 AS metric_value
FROM ts1
┌─entity─┬──────────────────dt─┬────────────ts─┬─metric────────┬─metric_name─┬─metric_value─┐
│ cpu │ 2017-10-28 23:06:50 │ 1509232010254 │ ('load',0.85) │ load │ 0.85 │
│ cpu │ 2017-10-28 23:06:50 │ 1509232010254 │ ('temp',68) │ temp │ 68 │
└────────┴─────────────────────┴───────────────┴───────────────┴─────────────┴──────────────┘
Since CH has lots of useful date and time functions, along with higher order functions and tuples, I think it's almost a natural time-series database.
It would probably be better to modify your schema to have 4 columns:
"some_entity_id", "timestamp", "metric_name", "metric_value"
You can include "metric_name" in the MergeTree index, to improve performance when searching for a specific metric of an entity. Test with and without it, to see if it's useful for the kind of queries you make.