Advanced InfluxDB Line Protocol settings

This documentation provides aid for those venturing outside of the path laid down by their language clients.

For the introductory InfluxDB Line Protocol materials, including authentication, see the ILP overview.

For the the basics of ingestion, instead consult the Ingestion overview.

Syntax

Each InfluxDB Line Protocol message has to end with a new line \n character.

table_name,symbolset columnset timestamp\n

Element	Definition
table_name	Name of the table where QuestDB will write data.
symbolset	A set of comma-separated name=value pairs that will be parsed as symbol columns.
columnset	A set of comma-separated name=value pairs that will be parsed as non-symbol columns.
timestamp	UNIX timestamp. The default unit is nanosecond and is configurable via line.tcp.timestamp. The value will be truncated to microsecond resolution when parsed by QuestDB.

name in the name=value pair always corresponds to column name in the table.

Behavior

• When the table_name does not correspond to an existing table, QuestDB will create the table on the fly using the name provided. Column types will be automatically recognized and assigned based on the data.
• The timestamp column is automatically created as designated timestamp with the partition strategy set to DAY. Alternatively, use CREATE TABLE to create the table with a different partition strategy before ingestion.
• When the timestamp is empty, QuestDB will use the server timestamp.

Generic example

Let's assume the following data:

timestamp	city	temperature	humidity	make
1465839830100400000	London	23.5	0.343	Omron
1465839830100600000	Bristol	23.2	0.443	Honeywell
1465839830100700000	London	23.6	0.358	Omron

The line protocol syntax for that table is:

readings,city=London,make=Omron temperature=23.5,humidity=0.343 1465839830100400000\n
readings,city=Bristol,make=Honeywell temperature=23.2,humidity=0.443 1465839830100600000\n
readings,city=London,make=Omron temperature=23.6,humidity=0.348 1465839830100700000\n

This would create table similar to this SQL statement and populate it.

CREATE TABLE readings (
  timestamp TIMESTAMP,
  city SYMBOL,
  temperature DOUBLE,
  humidity DOUBLE,
  make SYMBOL
) TIMESTAMP(timestamp) PARTITION BY DAY;

Designated timestamp

Timestamps

Designated timestamp is the trailing value of an InfluxDB Line Protocol message. It is optional, and when present, is a timestamp in Epoch nanoseconds. When the timestamp is omitted, the server will insert each message using the system clock as the row timestamp. See cairo.timestamp.locale and line.tcp.timestamp configuration options.

caution

• While columnset timestamp type units are microseconds, the designated timestamp units are nanoseconds by default, and can be overridden via the line.tcp.timestamp configuration property.

• The native timestamp format used by QuestDB is a Unix timestamp in microsecond resolution; timestamps in nanoseconds will be parsed and truncated to microseconds.

• For HTTP, precision parameters can added to a request. These include n or ns for nanoseconds, u or us formicroseconds, ms for milliseconds, s for seconds, m for minutes and h for hours. Otherwise, it will default to nanoseconds.

curl -i -XPOST 'http://localhost:9000/write?db=mydb&precision=s' \
--data-binary 'weather,location=us-midwest temperature=82 1465839830100400200'

Example of InfluxDB Line Protocol message with desginated timestamp value

tracking,loc=north val=200i 1000000000\n

Example of InfluxDB Line Protocol message sans timestamp

tracking,loc=north val=200i\n

note

We recommend populating designated timestamp via trailing value syntax above.

It is also possible to populate designated timestamp via columnset. Please see mixed timestamp reference.

Irregularly-structured data

InfluxDB line protocol makes it possible to send data under different shapes. Each new entry may contain certain tags or fields, and others not. QuestDB supports on-the-fly data structure changes with minimal overhead. Whilst the example just above highlights structured data, it is possible for InfluxDB line protocol users to send data as follows:

readings,city=London temperature=23.2 1465839830100400000\n
readings,city=London temperature=23.6 1465839830100700000\n
readings,make=Honeywell temperature=23.2,humidity=0.443 1465839830100800000\n

This would result in the following table:

timestamp	city	temperature	humidity	make
1465839830100400000	London	23.5	NULL	NULL
1465839830100700000	London	23.6	NULL	NULL
1465839830100800000	NULL	23.2	0.358	Honeywell

tip

Whilst we offer this function for flexibility, we recommend that users try to minimize structural changes to maintain operational simplicity.

Duplicate column names

If line contains duplicate column names, the value stored in the table will be that from the first name=value pair on each line. For example:

trade,ticker=USD price=30,price=60 1638202821000000000\n

Price 30 is stored, 60 is ignored.

Name restrictions

Table name cannot contain any of the following characters: \n, \r, ?, ,, ”, ", \, /, :, ), (, +, *, %, ~, starting ., trailing ., or a non-printable char.

Column name cannot contain any of the following characters: \n, \r, ?, ., ,, ”, ", \\, /, :, ), (, +, -, \* %%, ~, or a non-printable char.

Both table name and column names are allowed to have spaces . These spaces have to be escaped with \. For example both of these are valid lines.

trade\ table,ticker=USD price=30,details="Latest price" 1638202821000000000\n

trade,symbol\ ticker=USD price=30,details="Latest price" 1638202821000000000\n

Symbolset

Area of the message that contains comma-separated set of name=value pairs for symbol columns. For example in a message like this:

trade,ticker=BTCUSD,venue=coinbase price=30,price=60 1638202821000000000\n

symbolset is ticker=BTCUSD,venue=coinbase. Please note the mandatory space between symbolset and columnset. Naming rules for columns are subject to duplicate rules and name restrictions.

Symbolset values

symbolset values are always interpreted as SYMBOL. Parser takes values literally so please beware of accidentally using high cardinality types such as 9092i or 1.245667. This will result in a significant performance loss due to large mapping tables.

symbolset values are not quoted. They are allowed to have special characters, such as (space), =, ,, \n, \r and \, which must be escaped with a \. Example:

trade,ticker=BTC\\USD\,All,venue=coin\ base price=30 1638202821000000000\n

Whenever symbolset column does not exist, it will be added on-the-fly with type SYMBOL. On other hand when the column does exist, it is expected to be of SYMBOL type, otherwise the line is rejected.

Columnset

Area of the message that contains comma-separated set of name=value pairs for non-symbol columns. For example in a message like this:

trade,ticker=BTCUSD priceLow=30,priceHigh=60 1638202821000000000\n

columnset is priceLow=30,priceHigh=60. Naming rules for columns are subject to duplicate rules and name restrictions.

Columnset values

columnset supports several values types, which are used to either derive type of new column or mapping strategy when column already exists. These types are limited by existing InfluxDB Line Protocol specification. Wider QuestDB type system is available by creating table via SQL upfront. The following are supported value types: Integer, Long256, Float, String and Timestamp

Inserting NULL values

To insert a NULL value, skip the column (or symbol) for that row.

For example:

table1 a=10.5 1647357688714369403
table1 b=1.25 1647357698714369403

Will insert as:

a	b	timestamp
10.5	NULL	2022-03-15T15:21:28.714369Z
NULL	1.25	2022-03-15T15:21:38.714369Z

InfluxDB Line Protocol Datatypes and Casts

Strings vs Symbols

Strings may be recorded as either the STRING type or the SYMBOL type.

Inspecting a sample message we can see how a space ' ' separator splits SYMBOL columns to the left from the rest of the columns.

table_name,col1=symbol_val1,col2=symbol_val2 col3="string val",col4=10.5
                                            ┬
                                            ╰───────── separator

In this example, columns col1 and col2 are strings written to the database as SYMBOLs, whilst col3 is written out as a STRING.

SYMBOLs are strings which are automatically interned by the database on a per-column basis. You should use this type if you expect the string to be re-used over and over, such as is common with identifiers.

For one-off strings use STRING columns which aren't interned.

Casts

QuestDB types are a superset of those supported by InfluxDB Line Protocol. This means that when sending data you should be aware of the performed conversions.

See:

• QuestDB Types in SQL
• InfluxDB Line Protocol types and cast conversion tables

Constructing well-formed messages

Different library implementations will perform different degrees of content validation upfront before sending messages out. To avoid encountering issues, follow these guidelines:

• All strings must be UTF-8 encoded.

• Each column should only be specified once per row..

• Symbol columns must be written out before other columns.

• Table and column names can't have invalid characters. These should not contain ?, .,,, ', ", \, /, :, (, ), +, -, *, %, ~,' ' (space), \0 (nul terminator), ZERO WIDTH NO-BREAK SPACE.

• Write timestamp column via designated API, or at the end of the message if you are using raw sockets. If you have multiple timestamp columns write additional ones as column values.

• Don't change column type between rows.

Error handling

QuestDB will always log any InfluxDB Line Protocol errors in its server logs.

It is recommended that sending applications reuse TCP connections. If QuestDB receives an invalid message, it will discard invalid lines, produce an error message in the logs and forcibly disconnect the sender to prevent further data loss.

Data may be discarded because of:

• missing new line characters at the end of messages
• an invalid data format such as unescaped special characters
• invalid column / table name characters
• schema mismatch with existing tables
• message size overflows on the input buffer
• system errors such as no space left on the disk

Detecting malformed input can be achieved through QuestDB logs by searching for LineTcpMeasurementScheduler and LineTcpConnectionContext, for example:

2022-02-03T11:01:51.007235Z I i.q.c.l.t.LineTcpMeasurementScheduler could not create table [tableName=trades, ex=`column name contains invalid characters [colName=trade_%]`, errno=0]

The following input is tolerated by QuestDB:

• a column is specified twice or more on the same line, QuestDB will pick the first occurrence and ignore the rest
• missing columns, their value will be defaulted to null/0.0/false depending on the type of the column
• missing designated timestamp, the current server time will be used to generate the timestamp
• the timestamp is specified as a column instead of appending it to the end of the line
• timestamp appears as a column and is also present at the end of the line, the value sent as a field will be used

With sufficient client-side validation, the lack of errors to the client and confirmation isn't necessarily a concern: QuestDB will log out any issues and disconnect on error. The database will process any valid lines up to that point and insert rows.

To resume WAL table ingestion after recovery from errors, see ALTER TABLE RESUME WAL for more information.

If you don't immediately see data

If you don't see your inserted data, this is usually a result of one of two things:

• You prepared the messages, but forgot to call .flush() or similar in your client library, so no data was sent.

• The internal timers and buffers within QuestDB did not commit the data yet. For development (and development only), you may want to tweak configuration settings to commit data more frequently.

  cairo.max.uncommitted.rows=1

  Refer to InfluxDB Line Protocol's configuration documentation for more on these configuration settings.