A Comprehensive Analysis of Open-Source Time Series Databases (3)


Basic Concepts

INSERT machine_metric,cluster=Cluster-A,hostname=host-a cpu=10 1501554197019201823
SELECT * FROM "machine_metric" WHERE time > now() - 1h;  
SELECT * FROM "machine_metric" WHERE "cluster" = "Cluster-A" AND time > now() - 1h;
SELECT * FROM "machine_metric" WHERE "cluster" = "Cluster-A" AND cpu > 5 AND time > now() - 1h;


Continuous Query

CREATE CONTINUOUS QUERY "mean_cpu" ON "machine_metric_db"
SELECT mean("cpu") INTO "average_machine_cpu_5m" FROM "machine_metric" GROUP BY time(5m),cluster,hostname

TimeSeries Index

InfluxDB actually looks like two databases in one: a time series data store and an inverted index for the measurement, tag, and field metadata.

Memory-Based Index

// Measurement represents a collection of time series in a database. It also
// contains in memory structures for indexing tags. Exported functions are
// goroutine safe while un-exported functions assume the caller will use the
// appropriate locks.
type Measurement struct {
database string
Name string `json:"name,omitempty"`
name []byte // cached version as []byte
mu sync.RWMutex
fieldNames map[string]struct{}
// in-memory index fields
seriesByID map[uint64]*Series // lookup table for series by their id
seriesByTagKeyValue map[string]map[string]SeriesIDs // map from tag key to value to sorted set of series ids
// lazyily created sorted series IDs
sortedSeriesIDs SeriesIDs // sorted list of series IDs in this measurement
// Series belong to a Measurement and represent unique time series in a database.
type Series struct {
mu sync.RWMutex
Key string
tags models.Tags
ID uint64
measurement *Measurement
shardIDs map[uint64]struct{} // shards that have this series defined

Disk-Based Index




Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store