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Update existing data

This tutorial shows you how to update data in a datasource by overwriting existing data and adding new data to the datasource.

Prerequisites

Before starting this tutorial, download and run Apache Druid on your local machine as described in the single-machine quickstart.

You should also be familiar with the material in the following tutorials:

Load initial data

Load an initial data set to which you will overwrite and append data.

The ingestion spec is located at quickstart/tutorial/updates-init-index.json. This spec creates a datasource called updates-tutorial and ingests data from quickstart/tutorial/updates-data.json.

Submit the ingestion task:

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

Start the SQL command-line client:

bin/dsql

Run the following SQL query to retrieve data from updates-tutorial:

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

The datasource contains three rows of data with an animal dimension and a number metric.

Overwrite data

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

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

In the overwrite ingestion spec, notice the following:

  • The intervals field remains the same: "intervals" : ["2018-01-01/2018-01-03"]
  • New data is loaded from the local file, quickstart/tutorial/updates-data2.json
  • appendToExisting is set to false, indicating an overwrite task

Submit the ingestion task to overwrite the data:

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, run the SELECT query again. In the new results, the tiger row now has the value lion, the aardvark row has a different number, and the giraffe row has been replaced with a bear row.

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

Combine existing data with new data and overwrite

Now append new data to the updates-tutorial datasource from quickstart/tutorial/updates-data3.json using the ingestion spec quickstart/tutorial/updates-append-index.json.

The spec directs Druid to read from the existing updates-tutorial datasource as well as the quickstart/tutorial/updates-data3.json file. The task combines data from the two input sources, then overwrites the original data with the new combined data.

Submit that task:

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, it adds the new rows to the datasource. Run the SELECT query again. Druid automatically rolls up the data at ingestion time, aggregating the data in the lion row:

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

Append data

Now you append data to the datasource without changing the existing data. Use the ingestion spec located at quickstart/tutorial/updates-append-index2.json.

The spec directs Druid to ingest data from quickstart/tutorial/updates-data4.json and append it to the updates-tutorial datasource. The property appendToExisting is set to true in this spec.

Submit the task:

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

Druid adds two additional rows after octopus. When the task completes, query the data again to see them. Druid doesn't roll up the new bear row with the existing bear row because it stored the new data in a separate segment.

dsql> SELECT * FROM "updates-tutorial";
┌──────────────────────────┬──────────┬───────┬────────┐
│ __time                   │ animal   │ count │ number │
├──────────────────────────┼──────────┼───────┼────────┤
│ 2018-01-01T01:01:00.000Z │ lion     │     2 │    400 │
│ 2018-01-01T03:01:00.000Z │ aardvark │     1 │   9999 │
│ 2018-01-01T04:01:00.000Z │ bear     │     1 │    111 │
│ 2018-01-01T05:01:00.000Z │ mongoose │     1 │    737 │
│ 2018-01-01T06:01:00.000Z │ snake    │     1 │   1234 │
│ 2018-01-01T07:01:00.000Z │ octopus  │     1 │    115 │
│ 2018-01-01T04:01:00.000Z │ bear     │     1 │    222 │
│ 2018-01-01T09:01:00.000Z │ falcon   │     1 │   1241 │
└──────────────────────────┴──────────┴───────┴────────┘
Retrieved 8 rows in 0.02s.

Run the following groupBy query to see that the bear rows group together at query time:

dsql> SELECT __time, animal, SUM("count"), SUM("number") FROM "updates-tutorial" GROUP BY __time, animal;
┌──────────────────────────┬──────────┬────────┬────────┐
│ __time                   │ animal   │ EXPR$2 │ EXPR$3 │
├──────────────────────────┼──────────┼────────┼────────┤
│ 2018-01-01T01:01:00.000Z │ lion     │      2 │    400 │
│ 2018-01-01T03:01:00.000Z │ aardvark │      1 │   9999 │
│ 2018-01-01T04:01:00.000Z │ bear     │      2 │    333 │
│ 2018-01-01T05:01:00.000Z │ mongoose │      1 │    737 │
│ 2018-01-01T06:01:00.000Z │ snake    │      1 │   1234 │
│ 2018-01-01T07:01:00.000Z │ octopus  │      1 │    115 │
│ 2018-01-01T09:01:00.000Z │ falcon   │      1 │   1241 │
└──────────────────────────┴──────────┴────────┴────────┘
Retrieved 7 rows in 0.23s.
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