Explore key concepts of writing and querying data in InfluxDB. Assess your understanding of data structure, common commands, and fundamental best practices for efficient time series data management.
Which component must be present when writing a data point with line protocol in InfluxDB, as shown in the example temperature,sensor=s1 value=23.5 1667232000?
Explanation: The measurement name is mandatory when writing line protocol, as it specifies where data is stored. The other fields like database user and password are not part of the line protocol but are used for authentication. Retention policy can be optional and specified separately or as part of the target, but not directly in the point. Without the measurement name, InfluxDB cannot determine where to store the data.
In InfluxDB, what is the main difference between a tag and a field in a data point?
Explanation: Tags are indexed, making queries involving tags much faster, while fields hold the actual data values and are not indexed. Tags and fields can both store various types of data, not just numbers or text. Tags need not be unique per series, and fields do not determine time precision; timestamps handle precision.
How should two data points be written in a single line protocol payload to batch them in one write request?
Explanation: Each data point should be written on its own line and separated by a line break to batch them in a single request. Using a semicolon or a comma within the same line is not valid syntax and will not be properly parsed. The order of points by time is flexible; reversing time order is not required.
If a timestamp is omitted when writing a data point to InfluxDB, what happens?
Explanation: When no timestamp is included, the server automatically applies the current system time to the data point. The request is not rejected, and the timestamp is not set to zero. There is no warning or error since using system time is expected behavior in such cases.
Which statement retrieves all fields from the temperature measurement for the last 12 hours?
Explanation: The correct syntax uses SELECT * to fetch all fields, FROM designates the measurement, and the time condition specifies the past 12 hours. The distractor options use incorrect commands or syntax not supported by the query language, making them invalid.
What happens if you write a new data point with the same measurement, timestamp, and tag set as an existing point?
Explanation: When a point with identical measurement, tag set, and timestamp is written, the field values are overwritten with the newly written data. The database does not store both points or create duplicates. No error is produced, as overwriting is the intended behavior for such cases.
When writing data to InfluxDB without specifying a retention policy, where is the data stored by default?
Explanation: If no retention policy is specified, data is stored in the default policy named 'autogen'. Temporary buffers are used internally but do not hold persistent data. The data is not discarded, and there is no default retention policy called 'infinite'.
Which of the following is a valid field value type in InfluxDB?
Explanation: Strings are a supported field value type, along with numbers and booleans. Date, blob, and array types are not valid for field values; attempting to write fields with these types would result in errors or incorrect storage.
What does adding LIMIT 5 to the end of an InfluxDB SELECT query do?
Explanation: Using LIMIT 5 in a query restricts the result set to the first 5 entries that match the criteria. The clause does not relate to data size, tag count, or the number of distinct measurements retrieved in the query.
Which command removes all data from a measurement called humidity?
Explanation: The proper way to remove all data from a measurement is the DROP MEASUREMENT command. DELETE MEASUREMENT is not recognized in the language, nor are REMOVE or CLEAR. The DROP command ensures all associated series and data are deleted for that measurement.