Handle duplicate data points
InfluxDB identifies unique data points by their measurement, tag set, and timestamp (each a part of Line protocol used to write data to InfluxDB).
web,host=host2,region=us_west firstByte=15.0 1559260800000000000 --- ------------------------- ------------------- | | | Measurement Tag set TimestampDuplicate data points
For points that have the same measurement name, tag set, and timestamp, InfluxDB creates a union of the old and new field sets. For any matching field keys, InfluxDB uses the field value of the new point. For example:
# Existing data point web,host=host2,region=us_west firstByte=24.0,dnsLookup=7.0 1559260800000000000 # New data point web,host=host2,region=us_west firstByte=15.0 1559260800000000000After you submit the new data point, InfluxDB overwrites firstByte with the new field value and leaves the field dnsLookup alone:
# Resulting data point web,host=host2,region=us_west firstByte=15.0,dnsLookup=7.0 1559260800000000000from(bucket: "example-bucket") |> range(start: 2019-05-31T00:00:00Z, stop: 2019-05-31T12:00:00Z) |> filter(fn: (r) => r._measurement == "web") Table: keys: [_measurement, host, region] _time _measurement host region dnsLookup firstByte -------------------- ------------ ----- ------- --------- --------- 2019-05-31T00:00:00Z web host2 us_west 7 15Preserve duplicate points
To preserve both old and new field values in duplicate points, use one of the following strategies:
Add an arbitrary tag
Add an arbitrary tag with unique values so InfluxDB reads the duplicate points as unique.
For example, add a uniq tag to each data point:
# Existing point web,host=host2,region=us_west,uniq=1 firstByte=24.0,dnsLookup=7.0 1559260800000000000 # New point web,host=host2,region=us_west,uniq=2 firstByte=15.0 1559260800000000000It is not necessary to retroactively add the unique tag to the existing data point. Tag sets are evaluated as a whole. The arbitrary uniq tag on the new point allows InfluxDB to recognize it as a unique point. However, this causes the schema of the two points to differ and may lead to challenges when querying the data.
After writing the new point to InfluxDB:
from(bucket: "example-bucket") |> range(start: 2019-05-31T00:00:00Z, stop: 2019-05-31T12:00:00Z) |> filter(fn: (r) => r._measurement == "web") Table: keys: [_measurement, host, region, uniq] _time _measurement host region uniq firstByte dnsLookup -------------------- ------------ ----- ------- ---- --------- --------- 2019-05-31T00:00:00Z web host2 us_west 1 24 7 Table: keys: [_measurement, host, region, uniq] _time _measurement host region uniq firstByte -------------------- ------------ ----- ------- ---- --------- 2019-05-31T00:00:00Z web host2 us_west 2 15Increment the timestamp
Increment the timestamp by a nanosecond to enforce the uniqueness of each point.
# Old data point web,host=host2,region=us_west firstByte=24.0,dnsLookup=7.0 1559260800000000000 # New data point web,host=host2,region=us_west firstByte=15.0 1559260800000000001After writing the new point to InfluxDB:
from(bucket: "example-bucket") |> range(start: 2019-05-31T00:00:00Z, stop: 2019-05-31T12:00:00Z) |> filter(fn: (r) => r._measurement == "web") Table: keys: [_measurement, host, region] _time _measurement host region firstByte dnsLookup ------------------------------ ------------ ----- ------- --------- --------- 2019-05-31T00:00:00.000000000Z web host2 us_west 24 7 2019-05-31T00:00:00.000000001Z web host2 us_west 15The output of examples queries in this article has been modified to clearly show the different approaches and results for handling duplicate data.
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