Tutorial: Updating existing data

This tutorial demonstrates how to update existing data, showing both overwrites and appends.

For this tutorial, we’ll assume you’ve already downloaded Apache Druid as described in the single-machine quickstart and have it running on your local machine.

It will also be helpful to have finished Tutorial: Loading a file, Tutorial: Querying data, and Tutorial: Rollup.

Overwrite

This section of the tutorial will cover how to overwrite an existing interval of data.

Load initial data

Let’s load an initial data set which we will overwrite and append to.

The spec we’ll use for this tutorial is located at quickstart/tutorial/updates-init-index.json. This spec creates a datasource called updates-tutorial from the quickstart/tutorial/updates-data.json input file.

Let’s submit that task:

  1. bin/post-index-task --file quickstart/tutorial/updates-init-index.json --url http://localhost:8081

We have three initial rows containing an “animal” dimension and “number” metric:

  1. dsql> select * from "updates-tutorial";
  2. ┌──────────────────────────┬──────────┬───────┬────────┐
  3. │ __time                   │ animal   │ count │ number │
  4. ├──────────────────────────┼──────────┼───────┼────────┤
  5. │ 2018-01-01T01:01:00.000Z │ tiger    │     1 │    100 │
  6. │ 2018-01-01T03:01:00.000Z │ aardvark │     1 │     42 │
  7. │ 2018-01-01T03:01:00.000Z │ giraffe  │     1 │  14124 │
  8. └──────────────────────────┴──────────┴───────┴────────┘
  9. Retrieved 3 rows in 1.42s.

Overwrite the initial data

To overwrite this data, we can submit another task for the same interval, but with different input data.

The quickstart/tutorial/updates-overwrite-index.json spec will perform an overwrite on the updates-tutorial datasource.

Note that this task reads input from quickstart/tutorial/updates-data2.json, and appendToExisting is set to false (indicating this is an overwrite).

Let’s submit that task:

  1. bin/post-index-task --file quickstart/tutorial/updates-overwrite-index.json --url http://localhost:8081

When Druid finishes loading the new segment from this overwrite task, the “tiger” row now has the value “lion”, the “aardvark” row has a different number, and the “giraffe” row has been replaced. It may take a couple of minutes for the changes to take effect:

  1. dsql> select * from "updates-tutorial";
  2. ┌──────────────────────────┬──────────┬───────┬────────┐
  3. │ __time                   │ animal   │ count │ number │
  4. ├──────────────────────────┼──────────┼───────┼────────┤
  5. │ 2018-01-01T01:01:00.000Z │ lion     │     1 │    100 │
  6. │ 2018-01-01T03:01:00.000Z │ aardvark │     1 │   9999 │
  7. │ 2018-01-01T04:01:00.000Z │ bear     │     1 │    111 │
  8. └──────────────────────────┴──────────┴───────┴────────┘
  9. Retrieved 3 rows in 0.02s.

Combine old data with new data and overwrite

Let’s try appending some new data to the updates-tutorial datasource now. We will add the data from quickstart/tutorial/updates-data3.json.

The quickstart/tutorial/updates-append-index.json task spec has been configured to read from the existing updates-tutorial datasource and the quickstart/tutorial/updates-data3.json file. The task will combine data from the two input sources, and then overwrite the original data with the new combined data.

Let’s submit that task:

  1. bin/post-index-task --file quickstart/tutorial/updates-append-index.json --url http://localhost:8081

When Druid finishes loading the new segment from this overwrite task, the new rows will have been added to the datasource. Note that roll-up occurred for the “lion” row:

  1. dsql> select * from "updates-tutorial";
  2. ┌──────────────────────────┬──────────┬───────┬────────┐
  3. │ __time                   │ animal   │ count │ number │
  4. ├──────────────────────────┼──────────┼───────┼────────┤
  5. │ 2018-01-01T01:01:00.000Z │ lion     │     2 │    400 │
  6. │ 2018-01-01T03:01:00.000Z │ aardvark │     1 │   9999 │
  7. │ 2018-01-01T04:01:00.000Z │ bear     │     1 │    111 │
  8. │ 2018-01-01T05:01:00.000Z │ mongoose │     1 │    737 │
  9. │ 2018-01-01T06:01:00.000Z │ snake    │     1 │   1234 │
  10. │ 2018-01-01T07:01:00.000Z │ octopus  │     1 │    115 │
  11. └──────────────────────────┴──────────┴───────┴────────┘
  12. Retrieved 6 rows in 0.02s.

Append to the data

Let’s try another way of appending data.

The quickstart/tutorial/updates-append-index2.json task spec reads input from quickstart/tutorial/updates-data4.json and will append its data to the updates-tutorial datasource. Note that appendToExisting is set to true in this spec.

Let’s submit that task:

  1. bin/post-index-task --file quickstart/tutorial/updates-append-index2.json --url http://localhost:8081

When the new data is loaded, we can see two additional rows after “octopus”. Note that the new “bear” row with number 222 has not been rolled up with the existing bear-111 row, because the new data is held in a separate segment.

  1. dsql> select * from "updates-tutorial";
  2. ┌──────────────────────────┬──────────┬───────┬────────┐
  3. │ __time                   │ animal   │ count │ number │
  4. ├──────────────────────────┼──────────┼───────┼────────┤
  5. │ 2018-01-01T01:01:00.000Z │ lion     │     2 │    400 │
  6. │ 2018-01-01T03:01:00.000Z │ aardvark │     1 │   9999 │
  7. │ 2018-01-01T04:01:00.000Z │ bear     │     1 │    111 │
  8. │ 2018-01-01T05:01:00.000Z │ mongoose │     1 │    737 │
  9. │ 2018-01-01T06:01:00.000Z │ snake    │     1 │   1234 │
  10. │ 2018-01-01T07:01:00.000Z │ octopus  │     1 │    115 │
  11. │ 2018-01-01T04:01:00.000Z │ bear     │     1 │    222 │
  12. │ 2018-01-01T09:01:00.000Z │ falcon   │     1 │   1241 │
  13. └──────────────────────────┴──────────┴───────┴────────┘
  14. Retrieved 8 rows in 0.02s.

If we run a GroupBy query instead of a select *, we can see that the “bear” rows will group together at query time:

  1. dsql> select __time, animal, SUM("count"), SUM("number") from "updates-tutorial" group by __time, animal;
  2. ┌──────────────────────────┬──────────┬────────┬────────┐
  3. │ __time                   │ animal   │ EXPR$2 │ EXPR$3 │
  4. ├──────────────────────────┼──────────┼────────┼────────┤
  5. │ 2018-01-01T01:01:00.000Z │ lion     │      2 │    400 │
  6. │ 2018-01-01T03:01:00.000Z │ aardvark │      1 │   9999 │
  7. │ 2018-01-01T04:01:00.000Z │ bear     │      2 │    333 │
  8. │ 2018-01-01T05:01:00.000Z │ mongoose │      1 │    737 │
  9. │ 2018-01-01T06:01:00.000Z │ snake    │      1 │   1234 │
  10. │ 2018-01-01T07:01:00.000Z │ octopus  │      1 │    115 │
  11. │ 2018-01-01T09:01:00.000Z │ falcon   │      1 │   1241 │
  12. └──────────────────────────┴──────────┴────────┴────────┘
  13. Retrieved 7 rows in 0.23s.