classicvalues/bqwt

BigQuery Windowed Tables

BigQuery Windowed Tables (bqwt)

This library is compatible with Go 1.11+

Please refer to CHANGELOG.md if you encounter breaking changes.

• Motivation

Motivation

Ability to process incrementally incoming data in a way that is both duplication free and cost-effective is of paramount importance, especially when data is loaded or streamed to BigQuery in real time. When dealing with many tables at once managing processing state can add yet additional aspect that needs to be taken care. This library was developed to simplify multi tables time windowing processing. It can be deployed as stand alone service or as cloud function.

Introduction

Big Query provides a mechanism allowing windowing data ingested within the last 7 days with range decorators.

Syntax:

SELECT * PROJECT_ID:DATASET.TABLE@<timeFrom>-<timeTo>

References table data added between and , in milliseconds since the epoch.

• and must be within the last 7 days.

One important factor driving Big Query table layout design that needs to be taken into account is that the range decorators are only supported with Legacy SQL, meaning that standardSQL supported partition and clustered tables can not be windowed with this method currently.

In the absence of partition and clustering the following table design layout should provide good flexibility:

• DATASET.TABLE_[DATE_SUFFIX]
• DATASET.TABLE_[PARTITION_SHARD]_[DATE_SUFFIX]

In both of the scenarios it is possible to use table template in case when data is streamed to Big Query.

This project uses a meta file to store time windowed table processing state.

@metafile

{
  "URL": "gs://mybucket/xmeta",
  "DatasetID": "my-project:mydataset",
  "Tables": [
    {
      "ID": "mydataset.my_table_10_20181227",
      "ProjectID": "my-project",
      "Name": "my_table_10_20181227",
      "Dataset": "mydataset",
      "Window": {
        "From": "2018-12-27T16:00:37.802Z",
        "To": "2018-12-27T17:00:15.832Z"
      },
      "LastChangedFlag": "2018-12-27T17:00:57.238680333Z",
      "Changed": true,
      "Expression": "[mydataset.my_table_10_20181227@1545926437802-1545930015832]",
      "AbsoluteExpression": "[my-project:mydataset.my_table_10_20181227@1545926437802-1545930015832]"
    },
      {
          "ID": "mydataset.my_table_10_20181226",
          "ProjectID": "my-project",
          "Name": "my_table_10_20181226",
          "Dataset": "mydataset",
          "Window": {
            "From": "2018-12-26T16:00:37.802Z",
            "To": "2018-12-26T17:00:15.832Z"
          },
          "LastChangedFlag": "2018-12-26T17:00:57.238680333Z",
          "Changed": false
        }
  ],
  "Expression": "[mydataset.my_table_10_20181227@1545926437802-1545930015832]",
  "AbsoluteExpression": "[my-project:mydataset.my_table_10_20181227@1545926437802-1545930015832]"
}

Model

• WindowTable

type WindowedTable struct {
	ID                 string
	ProjectID          string
	Name               string
	Dataset            string
	Window             *TimeWindow `description:"recent change range: from, to timestamp"`
	LastChanged    time.Time 
	Changed            bool
	Expression         string `description:"represents table ranged decorator expression"`
	AbsoluteExpression string `description:"represents absolute table path ranged decorator expression"`
}

• Meta

type Meta struct {
	URL                 string
	DatasetID           string
	Tables              []*WindowedTable 
	Expression          string `description:"represents recently changed tables ranged decorator relative expression (without project id)"`
	AbsoluteExpression  string `description:"represents recently changed tables ranged decorator absolute expression (with project id)"`

}

Service Contract

Service accepts both POST and GET http method

• POST method request

type Request struct {
	Mode                string   `description:"operation mode: r - take snapshot, w - persist snapshot"`
	MetaURL             string   `description:"meta-file location, if relative path is used it adds gs:// protocol"`
	Location            string   `description:"dataset location"`
	DatasetID           string   `description:"source dataset"`
	MatchingTables      []string `description:"matching table contain expression"`
	PruneThresholdInSec int      `description:"max allowed duration in sec for unchanged windowed tables before removing"`
	LoopbackWindowInSec int      `description:"dataset max loopback window for checking changed tables in supplied dataset"`
	Expression          bool     `description:"if expression flag is set it returns only relative expression (without poejct id)"`
	AbsoluteExpression  bool     `description:"if expression flag is set it returns only abslute  expression (with poejct id)"`
	Method              string   `description:"data insert method: stream or load by default"`
}

GET method query string parameters request mapping

• mode: Mode
• meta: MetaURL
• dataset: DatasetID
• match: MatchingTables
• location: Location
• prune: PruneThresholdInSec (min 7 days)
• loopback: LoopbackWindowInSec
• expr: Expression
• absExpr: AbsoluteExpression
• method: Method

i.e: http://endpoint/WindowedTable?mode=r&meta=mybucket/xmeta&dataset=db1&expr=true

Note that changing table eviction time triggers table modification, thus prune threshold can not be less then 7 days.

Window table snapshot

Mode request attribute controls table time window snapshot, where r: take a snapshot, w: persist snapshot.

Taking snapshot

• when metafile does not exist the service reads all matching table info and create temp metafile with range decorator expression
• when temp meta file exists the service returns range decorator expression from that file
• when meta file exists the services compute changes between metafile and recently updated table, it stores updated table info and range decorator expression in a temp metafile

Persisting snapshot

• temp meta file is persisted to meta file.

Multi Read One Write scenario

The following shows example dataset windowing timeline:

1. t0: data is streamed to Big Query
2. t1: Process X reads dataset snapshot between t0 and t1
   • WindowedTable?mode=r&meta=bucket/x/meta.json&dataset=project:dataset&expr=true'
3. t2: more data is streamed
4. t3: Process X completed t0 to t1 processing, flags t0-t1 completed
   • WindowedTable?mode=w&meta=bucket/x/meta.json&dataset=project:dataset&expr=true'
5. t4: more data is streamed
6. t5: Process X reads dataset snapshot between t2 and t4
   • WindowedTable?mode=r&meta=bucket/x/meta.json&dataset=project:dataset&expr=true'
7. t6: more data is streamed
8. t7: Process X tries to process data but something goes wrong, thus no update
9. t8: more data is streamed
10. t9: Process X again reads dataset snapshot between t2 and t4
    • WindowedTable?mode=r&meta=bucket/x/meta.json&dataset=project:dataset&expr=true'
11. t10: more data is streamed
12. t11: Process X completed t2 to t4 processing, flags t2-t4 completed
    • WindowedTable?mode=w&meta=bucket/x/meta.json&dataset=project:dataset&expr=true'

Usage

Stand alone app

	snapshoot1, err := getHttpBody("http://myEndpoint/WindowedTable?mode=r&meta=myBucket/meta&dataset=myDataset")
	if err != nil {
		log.Fatal(err)
	}

	if hasData :=  len(snapshoot1) > 0;hasData {
		SQL := "SELECT * FROM " + string(snapshoot1)
		fmt.Printf("%v\n", SQL)

		//Process query ....

		//Persist snapshot only if there were no processing error
		_, err = getHttpBody("http://myEndpoint/WindowedTable?mode=w&meta=myBucket/meta&dataset=myDataset")
		if err != nil {
			log.Fatal(err)
		}
	} 

Apache beam

SQL Provider Class

import com.google.common.base.Strings;
import org.apache.beam.sdk.options.ValueProvider;

import java.io.Serializable;

public class SQLProvider implements ValueProvider<String>, Serializable {

    private final String baseSQL;
    private final String windowedTableURL;
    private final String emptyDatasetSQL;

    public SQLProvider(String baseSQL, String windowedTableURL, String emptyDatasetSQL) {
        this.baseSQL = baseSQL;
        this.emptyDatasetSQL = emptyDatasetSQL;
        this.windowedTableURL = windowedTableURL;
    }


    @Override
    public String get() {
        String from = Helper.getHttpBody(windowedTableURL);
        if(Strings.isNullOrEmpty(from)) {
            from = emptyDatasetSQL;
        }
        return baseSQL.replace("$SOURCE", from);
    }

    @Override
    public boolean isAccessible() {
        return true;
    }
}

Pipeline integration

public class Main {
    
        public static final String EMPTY_QUERY = "SELECT * FROM (SELECT INTEGER(NULL) AS field1,  STRING(NULL) AS fieldN) WHERE 1 = 0";
        public static final String WINDOWED_TABLE_URL = "http://myEndpoint/WindowedTable?mode=r&meta=myBucket/meta&dataset=myDataset";
        public static final String SQL = "SELECT * FROM $SOURCE";
         public static final Strin TABLE = "myTable";
        
       public static void main(String[] args)  {
            
           ValueProvider<String> sqlProvider = new SQLProvider(SQL, WINDOWED_TABLE_URL, EMPTY_QUERY);
           Pipeline pipeline = Pipeline.create(options);
           PCollection<TableRow> collection = pipeline.apply("read data", BigQueryIO.readTableRows().fromQuery(sqlProvider).withTemplateCompatibility().withoutValidation());
           
           //add more processing collection transforms here ....
           
            WriteResult eventOutput = collection.apply("write data",
                           BigQueryIO.writeTableRows()
                                   .to(schema.getTempTable(false))
                                   .withSchema(Helper.getTableSchema())
                                   .withMethod(BigQueryIO.Write.Method.STREAMING_INSERTS)
                                   .withCreateDisposition(BigQueryIO.Write.CreateDisposition.CREATE_IF_NEEDED));


            //Persist window table snapshot after writing to a table
            collection.apply(Wait.on(eventOutput.getFailedInserts()))
                                   // Transforms each row inserted to an Integer of value 1
                                   .apply(ParDo.of(countRows()))
                                   .apply(Sum.integersGlobally())
                                   .apply(ParDo.of(new SnapshpotUpdater()));
       }

       
       
       public static class  SnapshpotUpdater extends DoFn<Integer, Void> implements Serializable{
                private final String notificationURL = "http://myEndpoint/WindowedTable?mode=w&meta=myBucket/meta&dataset=myDataset";
    
               @ProcessElement
               public void processElement(ProcessContext c) {
                   Helper.getHttpBody(notificationURL);
               }
      }
       
}    

Deployment

Stand alone service

git clone https://github.com/viant/bqwt.git
cd bqwt/server
go build  bqwt.go
./bqwt -port 8080

Docker service

git clone https://github.com/viant/bqwt.git
cd bqwt
docker build --no-cache -t viant/bqwt:1.0 .
cd docker/
docker-compose up -d

Google cloud function deployment

• gcloud auth login
• gcloud config set project PROJECT_ID
• gcloud functions deploy WindowedTable --entry-point Handle --runtime go111 --trigger-http

Known limitation

• Non partitioning/clustering Windowing table with range decorator is only supported with legacy SQL, thus only non-partition, non-clustered tables run in legacy mode at the moment.

• Substantial data delay with streaming insert method In case of using streaming insert method, data first arrive to streaming buffer, which retains recently inserted rows. While query engine has ability to read records directly from the streaming buffer, these records are not considered for copy, extract job or range decorators. With this in mind this API uses StreamingBuffer.OldestEntryTime - 1 as table time window upper bound.

Practically it may take a while (upto ~ 90 minutes) before data is finally extracted from streaming buffer to a table. Find out more about streaming lifecycle

Running e2e tests

Create a 'test' Big Query project and service account with admin permission. Enable ssh on test host and create localhost secret

Create a test BQ service account secrets, save it as ~/.secret/viant-e2e.json

Install e2e test runner

git clone https://github.com/viant/bqwt.git
cd bqwt/e2e
endly