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Introduction to Cloud Bigtable (Java)

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Introduction to Cloud Bigtable (Java)

1 hour universal_currency_alt 7 Credits

GSP1038

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Overview

Cloud Bigtable is Google's fully managed NoSQL Big Data database service. It's the same database that powers many core Google services, including Search, Analytics, Maps, and Gmail.

In this lab, you'll learn how to use Cloud Bigtable with the Java HBase client to query a dataset of geospatial timeseries data from the New York City bus system. For example, you'll query data that could create this heatmap of bus trips in Manhattan:

Heat map of New York city.

You'll learn how to

  • Avoid common mistakes with schema design
  • Import data in a sequence file
  • Query your data

Setup and requirements

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After a few moments, the Google Cloud console opens in this tab.

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About the dataset

You'll be using a New York City bus dataset. There are more than 300 bus routes and 5,800 vehicles following those routes. The dataset is a log that includes destination name, vehicle id, latitude, longitude, expected arrival time, and scheduled arrival time, and is made up of snapshots taken about every 10 minutes for June 2017.

Schema design

To get the best performance from Cloud Bigtable, you have to be thoughtful when you design your schema. Data in Cloud Bigtable is automatically sorted lexicographically, so if you design your schema well, querying for related data is very efficient. Cloud Bigtable allows for queries using point lookups by row key or row-range scans that return a contiguous set of rows. However, if your schema isn't well thought out, you might find yourself piecing together multiple row lookups, or worse, doing full table scans, which are extremely slow operations.

Note: It is common for tables to have billions of rows, so doing a full table scan could take several minutes and take away resources for other queries.

Plan out the queries

The data has a variety of information, but for this lab you will use the location and destination of the bus.

With that information, you could perform these queries:

  • Get the location of a single bus over a given hour.
  • Get a day's worth of data for a bus line or specific bus.
  • Find all the buses in a rectangle on a map.
  • Get the current locations of all the buses (if you were ingesting this data in real time).

This set of queries can't all be done together optimally. For example, if you are sorting by time, you can't do a scan based on a location without doing a full table scan. You need to prioritize based on the queries you most commonly run.

This lab will focus on optimizing and executing the following set of queries:

  • Get the locations of a specific vehicle over an hour.
  • Get the locations of an entire bus line over an hour.
  • Get the locations of all buses in Manhattan in an hour.
  • Get the most recent locations of all buses in Manhattan in an hour.
  • Get the locations of an entire bus line over the month.
  • Get the locations of an entire bus line with a certain destination over an hour.

Design the row key

Though you are working with a static dataset, you will design a schema for scalability. This allows you to stream more bus data into the table and have it still perform well.

Here is the proposed schema for the row key:

[Bus company/Bus line/Timestamp rounded down to the hour/Vehicle ID]. Each row has an hour of data, and each cell holds multiple time-stamped versions of the data.

For this lab, use one column family to keep things simple. Here is an example view of what the data looks like. The data is sorted by row key.

Row key cf:VehicleLocation.Latitude cf:VehicleLocation.Longitude ...
MTA/M86-SBS/1496275200000/NYCT_5824 40.781212 @20:52:54.0040.776163 @20:43:19.0040.778714 @20:33:46.00 -73.961942 @20:52:54.00-73.946949 @20:43:19.00-73.953731 @20:33:46.00 ...
MTA/M86-SBS/1496275200000/NYCT_5840 40.780664 @20:13:51.0040.788416 @20:03:40.00 -73.958357 @20:13:51.00 -73.976748 @20:03:40.00 ...
MTA/M86-SBS/1496275200000/NYCT_5867 40.780281 @20:51:45.0040.779961 @20:43:15.0040.788416 @20:33:44.00 -73.946890 @20:51:45.00-73.959465 @20:43:15.00-73.976748 @20:33:44.00 ...
... ... ... ...

Common mistake: You might think that making time the first value in the row key would be ideal, because you probably care about more recent data, and would want to run queries mainly around certain times. Doing this causes hotspots in the data, however, so compromise by putting time third. This makes some of your queries more difficult, but you need to do this in order to get the full performance Cloud Bigtable has to offer. Also, you probably don't need to get all buses for a certain time at once. Check out this talk by Twitter for information about how they optimized their schema.

Task 1. Create instance, table, and family

  1. Create a Cloud Bigtable table using Cloud Shell, which you can open by clicking the Activate Cloud Shell button in the upper righthand corner.
Activate Cloud Shell icon
  1. Set the following environment variables to make copying and pasting the lab commands easier:
INSTANCE_ID="bus-instance" CLUSTER_ID="bus-cluster" TABLE_ID="bus-data" CLUSTER_NODES=3 CLUSTER_ZONE="{{{ project_0.default_zone | ZONE }}}"

Cloud Shell comes with the tools that you'll use in this lab, the gcloud command-line tool, the cbt command-line interface, and Maven, already installed.

  1. Enable the Cloud Bigtable and Cloud Dataflow APIs by running this command:
gcloud services disable dataflow.googleapis.com gcloud services enable bigtable.googleapis.com bigtableadmin.googleapis.com dataflow.googleapis.com The Dataflow API is disabled and re-enabled to ensure it is enabled correctly as there are sometimes issues with auto-enablement.

Click Check my progress to verify the objective. Enable required APIs

  1. Create an instance by running the following command:
gcloud bigtable instances create $INSTANCE_ID \ --display-name=$INSTANCE_ID \ --cluster-config=id=$CLUSTER_ID,zone=$CLUSTER_ZONE,nodes=$CLUSTER_NODES

Click Check my progress to verify the objective. Create the Bigtable Instance

  1. After you create the instance, populate the cbt configuration file, then create a table and column family by running the following commands:
echo project = $GOOGLE_CLOUD_PROJECT > ~/.cbtrc echo instance = $INSTANCE_ID >> ~/.cbtrc cbt createtable $TABLE_ID cbt createfamily $TABLE_ID cf

Click Check my progress to verify the objective. Create the table and column family

Task 2. Import data

Next, import a set of sequence files for this lab.

  • Run the following commands to import the table:
NUM_WORKERS=5 gcloud beta dataflow jobs run import-bus-data-$(date +%s) \ --gcs-location gs://dataflow-templates/latest/GCS_SequenceFile_to_Cloud_Bigtable \ --num-workers=$NUM_WORKERS --max-workers=$NUM_WORKERS --region={{{ project_0.default_region | REGION }}} \ --parameters bigtableProject=$GOOGLE_CLOUD_PROJECT,bigtableInstanceId=$INSTANCE_ID,bigtableTableId=$TABLE_ID,sourcePattern=gs://cloud-bigtable-public-datasets/bus-data/*

If the import job fails, wait a minute and try again. Sometimes when enabling the APIs and creating the instances everything can take a minute to propagate.

Click Check my progress to verify the objective. Create Dataflow Job to Import data

Monitor the import

You can monitor the job in the Cloud Dataflow UI. Also, you can view the load on your Cloud Bigtable instance with its monitoring UI. It should take 5 minutes for the entire import.

Task 3. Get the code

  1. Clone the Git repository containing a Java file which you will use to perform various queries on the dataset:
git clone https://github.com/googlecodelabs/cbt-intro-java.git cd cbt-intro-java
  1. Change to Java 11 by running the following commands:
sudo update-java-alternatives -s java-1.11.0-openjdk-amd64 && export JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64/

Task 4. Perform a lookup

The first query to perform is a simple row lookup. You'll get the data for a bus on the M86-SBS line on June 1, 2017 from 12:00 am to 1:00 am. A vehicle with id NYCT_5824 is on the bus line then.

With that information, and knowing the schema design (Bus company/Bus line/Timestamp rounded down to the hour/Vehicle ID,) you can deduce that the row key is:

MTA/M86-SBS/1496275200000/NYCT_5824

BusQueries.java

private static final byte[] COLUMN_FAMILY_NAME = Bytes.toBytes("cf"); private static final byte[] LAT_COLUMN_NAME = Bytes.toBytes("VehicleLocation.Latitude"); private static final byte[] LONG_COLUMN_NAME = Bytes.toBytes("VehicleLocation.Longitude"); String rowKey = "MTA/M86-SBS/1496275200000/NYCT_5824"; Result getResult = table.get( new Get(Bytes.toBytes(rowKey)) .addColumn(COLUMN_FAMILY_NAME, LAT_COLUMN_NAME) .addColumn(COLUMN_FAMILY_NAME, LONG_COLUMN_NAME));

The result should contain the most recent location of the bus within that hour. But you want to see all the locations, so set the maximum number of versions on the get request.

BusQueries.java

Result getResult = table.get( new Get(Bytes.toBytes(rowKey)) .setMaxVersions(Integer.MAX_VALUE) .addColumn(COLUMN_FAMILY_NAME, LAT_COLUMN_NAME) .addColumn(COLUMN_FAMILY_NAME, LONG_COLUMN_NAME));
  • In the Cloud Shell, run the following command to get a list of latitudes and longitudes for that bus over the hour:
mvn package exec:java -Dbigtable.projectID=$GOOGLE_CLOUD_PROJECT \ -Dbigtable.instanceID=$INSTANCE_ID -Dbigtable.table=$TABLE_ID \ -Dquery=lookupVehicleInGivenHour Note: Visualization for each step, from Google Maps, is included so you can follow along. Instructions for how to use Google Maps is not in scope for this lab.

Here is the result for this first query:

A map of Manhattan with six points plotted.

Task 5. Perform a scan

What if you want to see all the data for the bus line for that hour. The scan code looks pretty similar to the get code. Give the scanner a starting position and then indicate you only want rows for the M86-SBS bus line within the hour denoted by the timestamp 1496275200000.

BusQueries.java

Scan scan; scan = new Scan(); scan.setMaxVersions(Integer.MAX_VALUE) .addColumn(COLUMN_FAMILY_NAME, LAT_COLUMN_NAME) .addColumn(COLUMN_FAMILY_NAME, LONG_COLUMN_NAME) .withStartRow(Bytes.toBytes("MTA/M86-SBS/1496275200000")) .setRowPrefixFilter(Bytes.toBytes("MTA/M86-SBS/1496275200000")); ResultScanner scanner = table.getScanner(scan);
  1. Run the following command to get the results:
mvn package exec:java -Dbigtable.projectID=$GOOGLE_CLOUD_PROJECT \ -Dbigtable.instanceID=$INSTANCE_ID -Dbigtable.table=$TABLE_ID \ -Dquery=scanBusLineInGivenHour A map of Manhattan with several more plots.

An interesting modification to this query is to view the entire month of data for the M86-SBS bus line, and this is very easy to do. Remove the timestamp from the start row and prefix filter to get the result.

BusQueries.java

scan.withStartRow(Bytes.toBytes("MTA/M86-SBS/")) .setRowPrefixFilter(Bytes.toBytes("MTA/M86-SBS/")); // Optionally, reduce the results to receive one version per column // since there are so many data points. scan.setMaxVersions(1);
  1. Run the following command to get the results. (There will be a long list of results.)
mvn package exec:java -Dbigtable.projectID=$GOOGLE_CLOUD_PROJECT \ -Dbigtable.instanceID=$INSTANCE_ID -Dbigtable.table=$TABLE_ID \ -Dquery=scanEntireBusLine The orange blobs on the map indicate the stops, and the bright red blobs are the start and end of the route. A heatmap of Manhattan.

Task 6. Introduce filters

Next, filter on buses heading east, buses heading west, and create a separate heatmap for each.

Note: This filter will only check the latest version, so you will set the max versions to one to ensure the results match the filter.

BusQueries.java

Scan scan; ResultScanner scanner; scan = new Scan(); SingleColumnValueFilter valueFilter = new SingleColumnValueFilter( COLUMN_FAMILY_NAME, Bytes.toBytes("DestinationName"), CompareOp.EQUAL, Bytes.toBytes("Select Bus Service Yorkville East End AV")); scan.setMaxVersions(1) .addColumn(COLUMN_FAMILY_NAME, LAT_COLUMN_NAME) .addColumn(COLUMN_FAMILY_NAME, LONG_COLUMN_NAME); scan.withStartRow(Bytes.toBytes("MTA/M86-SBS/")) .setRowPrefixFilter(Bytes.toBytes("MTA/M86-SBS/")); scan.setFilter(valueFilter); scanner = table.getScanner(scan);
  1. Run the following command to get the results for buses going east:
mvn package exec:java -Dbigtable.projectID=$GOOGLE_CLOUD_PROJECT \ -Dbigtable.instanceID=$INSTANCE_ID -Dbigtable.table=$TABLE_ID \ -Dquery=filterBusesGoingEast
  1. To get the buses going west, change the string in the valueFilter:

BusQueries.java

SingleColumnValueFilter valueFilter = new SingleColumnValueFilter( COLUMN_FAMILY_NAME, Bytes.toBytes("DestinationName"), CompareOp.EQUAL, Bytes.toBytes("Select Bus Service Westside West End AV"));
  1. Run the following command to get the results for buses going west:
mvn package exec:java -Dbigtable.projectID=$GOOGLE_CLOUD_PROJECT \ -Dbigtable.instanceID=$INSTANCE_ID -Dbigtable.table=$TABLE_ID \ -Dquery=filterBusesGoingWest

Buses heading east

Updated heatmap.

Buses heading west

Updated heatmap.

By comparing the two heatmaps, you can see the differences in the routes as well as notice differences in the pacing. One interpretation of the data is that on the route heading west, the buses are getting stopped more, especially when entering Central Park. And on the buses heading east, you don't really see many choke points.

Task 7. Perform a multi-range scan

For the final query, you'll address the case when you care about many bus lines in an area.

BusQueries.java

private static final String[] MANHATTAN_BUS_LINES = {"M1","M2","M3",... Scan scan; ResultScanner scanner; List ranges = new ArrayList<>(); for (String busLine : MANHATTAN_BUS_LINES) { ranges.add( new RowRange( Bytes.toBytes("MTA/" + busLine + "/1496275200000"), true, Bytes.toBytes("MTA/" + busLine + "/1496275200001"), false)); } Filter filter = new MultiRowRangeFilter(ranges); scan = new Scan(); scan.setFilter(filter); scan.setMaxVersions(Integer.MAX_VALUE) .addColumn(COLUMN_FAMILY_NAME, LAT_COLUMN_NAME) .addColumn(COLUMN_FAMILY_NAME, LONG_COLUMN_NAME); scan.withStartRow(Bytes.toBytes("MTA/M")).setRowPrefixFilter(Bytes.toBytes("MTA/M")); scanner = table.getScanner(scan);
  • Run the following command to get the results:
mvn package exec:java -Dbigtable.projectID=$GOOGLE_CLOUD_PROJECT \ -Dbigtable.instanceID=$INSTANCE_ID -Dbigtable.table=$TABLE_ID \ -Dquery=scanManhattanBusesInGivenHour The resulting heatmap.

Task 8. Clean up to avoid charges

Because you are working in a lab, when you end the lab all your resources and your project will be cleaned up and discarded for you. You should know how to clean up resources yourself to save on cost and to be a good cloud citizen.

gcloud bigtable instances delete $INSTANCE_ID

Click Check my progress to verify the objective. Delete the Bigtable Instance

Conclusion

You are now familiar with Cloud Bigtable and understand schema design; setting up an instance, table, and family; importing sequence files with dataflow; querying with a lookup, a scan, a scan with a filter, and a multi-range scan in Cloud Bigtable.

Next steps

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Manual Last Updated October 25, 2023

Lab Last Tested October 25, 2023

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