Planning Your Riak TS Table

You’ve installed Riak TS, and you’re ready to create a table.

  • If you’re just looking to test out Riak TS, you can jump ahead to Create a Table, and test out our sample table.
  • If you’re looking to set up your production environment, keep reading for guidelines on how best to structure your table.
  • If you’re looking for more information about what the components of a Riak TS table do, check out Table Architecture.
  • Riak TS tables are closely tied to SQL tables. If would like to know more about how Riak TS integrates SQL, check out SQL for Riak TS.
Important

The structure of your TS table will have a major impact on your Riak TS performance. Once created, your table cannot be changed. Please read through these sections carefully to determine the best options for your use-case.

TS Table Schema

Here is an example Riak TS CREATE TABLE statement, broken across many lines for clarity. (Remember, once created, your table cannot be changed):

CREATE TABLE GeoCheckin
(
  region       VARCHAR   NOT NULL,
  state        VARCHAR   NOT NULL,
  time         TIMESTAMP NOT NULL,
  weather      VARCHAR   NOT NULL,
  temperature  DOUBLE,
  PRIMARY KEY (
    (region, state, QUANTUM(time, 15, 'm')),
    region, state, time
  )
);

A TS table is made up of:

  • a table name, GeoCheckin in this example,
  • column definitions, the first 6 lines after the table name in this example, and
  • the primary key, which is everything following PRIMARY KEY in this example.

The column definitions will determine the columns of your TS table, while the primary key determines where data is stored in your TS cluster.

Table Limitations

You cannot create a table with more than 511 total columns. If you try to create a table with more than 511 columns, you will receive an error.

Column Definitions

Column definitions define the structure of the data and are comprised of three parts: a column name, a data type, and (optionally) an inline constraint.

column_name data_type [NOT NULL],

Column names (region, state, etc) must be ASCII strings, in addition to having the correct case. If column names need to contain spaces or punctuation they can be double quoted.

Any column names specified as part of the primary key must be defined as NOT NULL.

The column definitions for the keys can be specified in any order in the CREATE TABLE statement. For instance both are correct:

A.

CREATE TABLE GeoCheckin
(
  region       VARCHAR   NOT NULL,
  state        VARCHAR   NOT NULL,
  time         TIMESTAMP NOT NULL,
  weather      VARCHAR   NOT NULL,
  temperature  DOUBLE,
  PRIMARY KEY (
    (region, state, QUANTUM(time, 15, 'm')),
    region, state, time
  )
);

B.

CREATE TABLE GeoCheckin
(
   time         TIMESTAMP NOT NULL,
   state        VARCHAR   NOT NULL,
   weather      VARCHAR   NOT NULL,
   region       VARCHAR   NOT NULL,
   temperature  DOUBLE,
   PRIMARY KEY (
     (region, state, QUANTUM(time, 15, 'm')),
     region, state, time
  )
);

The data types in column definitions are limited. Valid types are:

  • VARCHAR - Any Latin 1 string content is valid. Can only be compared using strict equality, and will not be typecast (e.g., to an integer) for comparison purposes. Use single quotes to delimit varchar strings.
  • BOOLEAN - true or false (any case).
  • TIMESTAMP - Integer values expressing UNIX epoch time in UTC in milliseconds. Zero is not a valid timestamp.
  • SINT64 - Signed 64-bit integer.
  • DOUBLE - This type does not comply with its IEEE specification: NaN (not a number) and INF (infinity) cannot be used.
  • BLOB - A new type as of TS 1.5.2 for binary objects. Can be used to store any unstructured data “as is”, including JSON or binary data. It will be displayed as a hex value (and can be input as hex) via riak-shell. Not yet recommended for use in primary keys.

Primary Key

The PRIMARY KEY describes both the partition key and local key. The partition key is a prefix of the local key, consisting of one or more column names in parentheses. The local key must begin with the same column names as the partition key, but may also contain additional column names.

CREATE TABLE GeoCheckin
(
   region       VARCHAR   NOT NULL,
   state        VARCHAR   NOT NULL,
   time         TIMESTAMP NOT NULL,
   weather      VARCHAR   NOT NULL,
   temperature  DOUBLE,
   PRIMARY KEY (
     (region, state, QUANTUM(time, 15, 'm')),  <-- PARTITION KEY
      region, state, time                      <-- LOCAL KEY
   )
);

The field definitions for the PRIMARY KEY can be specified in any order in the CREATE TABLE statement. For instance both are correct:

A.

CREATE TABLE GeoCheckin
(
   region       VARCHAR   NOT NULL,
   state        VARCHAR   NOT NULL,
   time         TIMESTAMP NOT NULL,
   weather      VARCHAR   NOT NULL,
   temperature  DOUBLE,
   PRIMARY KEY (
     (region, state, time,
      region, state, time
   )
);

B.

CREATE TABLE GeoCheckin
(
   region       VARCHAR   NOT NULL,
   state        VARCHAR   NOT NULL,
   time         TIMESTAMP NOT NULL,
   weather      VARCHAR   NOT NULL,
   temperature  DOUBLE,
   PRIMARY KEY (
     (state, region, time,
      state, region, time, weather
   )
)

Partition Key

The partition key is the first element of the primary key, and must have at least one column name.

A general guideline is to first choose a column name that represents a class or type of data, and then choose a second column name that is a more specific instance(s) of the class/type.

You may specify a quantum, which is used to colocate data on one of the partition key’s timestamp fields:

PRIMARY KEY  ((region, state, QUANTUM(time, 1, 's')), ...)

If you choose to specify a quantum, you may specify only one and it must be the last element of the partition key.

The quantum function takes 3 parameters:

  • the name of a field in the table definition of type TIMESTAMP
  • a quantity as a positive integer, greater than zero
  • a unit of time:
    • 'd' - days
    • 'h' - hours
    • 'm' - minutes
    • 's' - seconds

If you choose to specify a quantum, the quantum you pick will greatly impact your query performance. Read more about quanta below.

Local Key

The local key comes after the partition key. It must first contain the same column names in the same order as the partition key. This ensures that the same column names determining your data’s partition also dictate the sorting of the data within that partition.

The local key may also contain additional column names so long as they come after the column names present in the partition key. For example:

   PRIMARY KEY (
     (region, QUANTUM(time, 15, 'm')),
      region, time, weather, temperature
   )

On Key Uniqueness

The local key in a TS row is what makes that row’s key/address unique from other rows. In the examples on this page and others we’ve used a composite key of region, state, time because it can model different devices and groupings.
If you have another integer identifier, such as a device ID, you can guarantee to be unique when combined with a timestamp, then you can have a shorter key definition.

The table definition for such a schema would be as follows:

CREATE TABLE GeoCheckin
(
   id           SINT64    NOT NULL,
   region       VARCHAR   NOT NULL,
   state        VARCHAR   NOT NULL,
   time         TIMESTAMP NOT NULL,
   weather      VARCHAR   NOT NULL,
   temperature  DOUBLE,
   PRIMARY KEY (
     (id, QUANTUM(time, 15, 'm')),  <-- PARTITION KEY
      id, time                      <-- LOCAL KEY
   )
)

The omission of region and state from the key definition makes it shorter, and will also make any SQL queries shorter because we’ll only need a minimum of id/time in our queries WHERE clauses (see Table Architecture and Querying Guidelines for all the specifics about how different partition + local key layouts change the way you query data).

The downside to this schema is that you’ll likely need to do one query per device, instead of being able to group multiple devices together based on their other defining characteristics such as region & state.

Please take care in defining how you address your unique data, as it will affect how you will query it in the future.

Sort With Local Keys

A table’s local key determines how it is stored and ordered on disk. Adding the ASC or DESC keywords to the local key lets you control the sort order of records on disk, and avoid sorting using ORDER BY or at the application level.

Ordering rows using ASC or DESC on the local key reduces workload on the cluster because no sorting is required when a query is executed. This may make using ASC or DESC on the local key a better choice than using ORDER BY.

The ASC or DESC keywords must be applied to the local key, not the partition key. The keywords can only be applied to SINT64, TIMESTAMP and VARCHAR columns.

Ascending Local Key Example

For example, with the following table and data:

CREATE TABLE ascending_table (
a SINT64 NOT NULL,
b TIMESTAMP NOT NULL,
PRIMARY KEY ((a, quantum(b, 1, 'm')), a, b));

INSERT INTO ascending_table VALUES (1,1);
INSERT INTO ascending_table VALUES (1,2);
INSERT INTO ascending_table VALUES (1,3);
INSERT INTO ascending_table VALUES (1,4);
INSERT INTO ascending_table VALUES (1,5);

Then query:

SELECT * FROM ascending_table WHERE a = 1 AND b >= 1 AND b <= 5;

+-+------------------------+
|a|           b            |
+-+------------------------+
|1|1970-01-01T00:00:00.001Z|
|1|1970-01-01T00:00:00.002Z|
|1|1970-01-01T00:00:00.003Z|
|1|1970-01-01T00:00:00.004Z|
|1|1970-01-01T00:00:00.005Z|
+-+------------------------+

The results are returned oldest first because the keys are ordered in ascending timestamp value.

Descending Local Key Example

If we’re building an application that shows events, such as orders or tweets, we probably want to show the latest results first.

For example:

CREATE TABLE descending_table (
a SINT64 NOT NULL,
b TIMESTAMP NOT NULL,
PRIMARY KEY ((a, quantum(b, 1, 'm')), a, b DESC));

INSERT INTO descending_table VALUES (1,1);
INSERT INTO descending_table VALUES (1,2);
INSERT INTO descending_table VALUES (1,3);
INSERT INTO descending_table VALUES (1,4);
INSERT INTO descending_table VALUES (1,5);

SELECT * FROM descending_table WHERE a = 1 AND b >= 1 AND b <= 5;

+-+------------------------+
|a|           b            |
+-+------------------------+
|1|1970-01-01T00:00:00.005Z|
|1|1970-01-01T00:00:00.004Z|
|1|1970-01-01T00:00:00.003Z|
|1|1970-01-01T00:00:00.002Z|
|1|1970-01-01T00:00:00.001Z|
+-+------------------------+

In the new descending_table, the DESC keyword has been added to b in the local key. When the table is queried, the results are returned in descending timestamp order, starting with the greatest timestamp.

Quantum

Choosing the right quantum for your Riak TS table is incredibly important, as it can optimize or diminish your query performance. The short guide is:

  1. If you care most about individual query latency, then spread your data around the cluster so a typical query spans all nodes, or
  2. If you care most about throughput, then localize your data so that typical queries are confined to single nodes, or
  3. If you can’t predict your usage or you have a mixed-use case, optimize for latency because the fractional latency gains of less data localization are much higher than the throughput losses.
  4. Finally, if you simply don’t know what you prefer, there’s more information in the section below to help you decide.

Your quanta use-case

The quantum is part of the partition key which is in the primary key, as discussed above.

   PRIMARY KEY (
     (region, QUANTUM(time, 15, 'm')),
      region, time, weather, temperature
   )

Quanta give you the ability to control how data is stored around your cluster, which impacts query performance. Determining the quantum that is best for you depends on how you expect to query your data and whether you care more about latency or throughput.

If you have a cluster that isn’t busy, a large query run on a single node will take longer to complete than the same query split into subqueries across multiple nodes. So if running individual queries as fast as possible is what you care most about (latency), you want a smaller quantum that will spread your data more evenly around the cluster.

However, if you added up the iteration times of those subqueries, you would find that the total is larger than your single-node iteration time. Multi-node queries take more added-up time overall because there’s extra overhead in setting up the subquery iterations. When you run a whole query on a single node, you incur that overhead only once.

This means that if you have a busy cluster, 5 large queries run against one node each will complete more quickly than those same 5 queries split into subqueries that run across all the nodes in your cluster. If executing as many queries as possible in the shortest time is what you care most about (throughput), you want a large enough quantum that the data for a typical query are localized to one node.

Latency

If you need to optimize your Riak TS performance to ensure that individual queries are run quickly (latency), rather than for many queries to be handled at once (throughput), then you will need to take advantage of the parallel resources in your cluster by splitting queries across multiple nodes.

The best quantum for latency

To optimize query latency, your quantum should be small enough that your normal-sized query is spread across all nodes. If your quantum is too small it can result in so many subqueries being generated per-node that the parallel-processing capacity of your nodes is overwhelmed.

If you’re up for a little math, you can use the following formula to identify the optimal quantum:

Q ~ t/N 

t is the time spanned by your typical query, N is the number of nodes in your cluster, and Q is your quantum.

For example, if you have a 5-node cluster and your typical query is for 40 hours of data, your quantum should be no larger than 8 hours:

8 = 40/5

If your quantum is larger than 8 hours, subqueries will execute on fewer than all 5 nodes.

You might be able to push your quantum a bit smaller, since each node in turn has some parallel processing capacity. Take care not to make it too small, or you’ll start to lose performance

For instance, in your 5-node cluster, with a typical query for 40 hours of data, and assuming 4 subqueries per node, you could make your quantum 2 hours which would further minimize your query latency.

However, a 1-hour quantum would be too small, because it would cause you to have 8 subqueries per node. These 8 subqueries would not execute in parallel; instead, they would effectively execute as two sets of 4 subqueries, one after the other, which is less efficient than a single set of 4 subqueries that are twice as long.

Throughput

If you need to optimize your Riak TS performance to handle many queries (throughput) more than you need those queries to be run quickly (latency), then you will want your data to be more localized.

How small should my quantum be?

To optimize for throughput, we suggest that your minimum quantum size be several times longer than your regular, individual query length. For the best performance, the typical query should span as few quanta as possible.

For example, if your typical query is an hour’s worth of data, then your quantum should be large enough that most (but not all) of your queries will only hit a single node. This would mean a quantum between 5 and 10 hours, which would result in 80% to 90% of your queries hitting a single node.

Take care not to let 100% of your queries hit a single node, however, or you risk crashing the node.

How large should my quantum be?

For the best throughput, we suggest that your maximum quantum size be chosen to minimize the number of concurrent queries hitting the same node. For the best performance, your quantum should be bounded by the total time spanned by your instantaneous volume of concurrent queries.

For example, if you are typically issuing thousands of concurrent queries for different hours of the same week’s worth of data, then you want your quantum to be significantly less than a week, or all your queries will end up hitting the same node and will execute serially, rather than benefit from parallelization in a distributed ring.

More information

After creating a table, its schema can be discovered with the DESCRIBE statement.

Still unsure how best to structure your Riak TS table? Check out our best practice recommendations.

Confused about what column definitions, primary key, etc. do? Check out Table Architecture for an in-depth explanation of TS tables.

Next Steps

Now that you know how your Riak TS table will be structured, you can move on to creating your table.