Add select docs and fix return values for Select API (#6300)

cmd/object-handlers.go

@@ -161,19 +161,22 @@ func (api objectAPIHandlers) SelectObjectContentHandler(w http.ResponseWriter, r
 		writeErrorResponse(w, ErrInvalidExpressionType, r.URL)
 		return
 	}
-	if len(selectReq.Expression) >= (256 * 1000) {
+	if len(selectReq.Expression) >= s3select.MaxExpressionLength {
 		writeErrorResponse(w, ErrExpressionTooLong, r.URL)
+		return
 	}
 	if selectReq.InputSerialization.CSV.FileHeaderInfo != CSVFileHeaderInfoUse &&
 		selectReq.InputSerialization.CSV.FileHeaderInfo != CSVFileHeaderInfoNone &&
 		selectReq.InputSerialization.CSV.FileHeaderInfo != CSVFileHeaderInfoIgnore &&
 		selectReq.InputSerialization.CSV.FileHeaderInfo != "" {
 		writeErrorResponse(w, ErrInvalidFileHeaderInfo, r.URL)
+		return
 	}
 	if selectReq.OutputSerialization.CSV.QuoteFields != CSVQuoteFieldsAlways &&
 		selectReq.OutputSerialization.CSV.QuoteFields != CSVQuoteFieldsAsNeeded &&
 		selectReq.OutputSerialization.CSV.QuoteFields != "" {
 		writeErrorResponse(w, ErrInvalidQuoteFields, r.URL)
+		return
 	}
 
 	getObject := objectAPI.GetObject
@@ -205,8 +208,7 @@ func (api objectAPIHandlers) SelectObjectContentHandler(w http.ResponseWriter, r
 	}
 	go func() {
 		defer reader.Close()
-		if gerr := getObject(ctx, bucket, object, 0, objInfo.Size, writer,
+		if gerr := getObject(ctx, bucket, object, 0, objInfo.Size, writer, objInfo.ETag); gerr != nil {
-			objInfo.ETag); gerr != nil {
 			pipewriter.CloseWithError(gerr)
 			return
 		}
@@ -243,10 +245,9 @@ func (api objectAPIHandlers) SelectObjectContentHandler(w http.ResponseWriter, r
 			writeErrorResponse(w, toAPIErrorCode(err), r.URL)
 			return
 		}
-		if err := s3s.Execute(w); err != nil {
+		if err = s3s.Execute(w); err != nil {
 			logger.LogIf(ctx, err)
 		}
-		return
 	}
 }
 

docs/select/README.md

@@ -0,0 +1,89 @@
+# Select API Quickstart Guide [![Slack](https://slack.minio.io/slack?type=svg)](https://slack.minio.io)
+Traditional retrieval of objects is always as whole entities, i.e GetObject for a 5 GiB object, will always return 5 GiB of data. S3 Select API allows us to retrieve a subset of data by using simple SQL expressions. By using Select API to retrieve only the data needed by the application, drastic performance improvements can be achieved.
+
+> This implementation is compatible with AWS S3 Select API
+
+## 1. Prerequisites
+- Install Minio Server from [here](http://docs.minio.io/docs/minio-quickstart-guide).
+- Familiarity with AWS S3 API
+- Familiarity with Python and installing dependencies.
+
+## 2. Install boto3
+Install `aws-sdk-python` from AWS SDK for Python official docs [here](https://aws.amazon.com/sdk-for-python/)
+
+## 3. Example
+As an example, let us take a gzip compressed CSV file. Without S3 Select, we would need to download, decompress and process the entire CSV to get the data you needed. With Select API, can use a simple SQL expression to return only the data from the CSV you’re interested in, instead of retrieving the entire object. Following Python example shows how to retrieve the first column `Location` from an object containing data in CSV format.
+
+Please replace ``endpoint_url``,``aws_access_key_id``, ``aws_secret_access_key``, ``Bucket`` and ``Key`` with your local setup in this ``select.py`` file.
+
+```py
+#!/usr/bin/env/env python3
+import boto3
+
+s3 = boto3.client('s3',
+                  endpoint_url='http://localhost:9000',
+                  aws_access_key_id='minio',
+                  aws_secret_access_key='minio123',
+                  region_name='us-east-1')
+
+r = s3.select_object_content(
+    Bucket='mycsvbucket',
+    Key='sampledata/TotalPopulation.csv.gz',
+    ExpressionType='SQL',
+    Expression="select * from s3object s where s.Location like '%United States%'",
+    InputSerialization={
+        'CSV': {
+            "FileHeaderInfo": "USE",
+        },
+        'CompressionType': 'GZIP',
+    },
+    OutputSerialization={'CSV': {}},
+)
+
+for event in r['Payload']:
+    if 'Records' in event:
+        records = event['Records']['Payload'].decode('utf-8')
+        print(records)
+    elif 'Stats' in event:
+        statsDetails = event['Stats']['Details']
+        print("Stats details bytesScanned: ")
+        print(statsDetails['BytesScanned'])
+        print("Stats details bytesProcessed: ")
+        print(statsDetails['BytesProcessed'])
+```
+
+## 4. Run the Program
+Upload first a sample dataset downloaded from [TotalPopulation.csv](https://esa.un.org/unpd/wpp/DVD/Files/1_Indicators%20(Standard)/CSV_FILES/WPP2017_TotalPopulationBySex.csv) using the following commands.
+```sh
+$ curl "https://esa.un.org/unpd/wpp/DVD/Files/1_Indicators%20(Standard)/CSV_FILES/WPP2017_TotalPopulationBySex.csv" > TotalPopulation.csv
+$ mc mb myminio/mycsvbucket
+$ gzip TotalPopulation.csv
+$ mc cp TotalPopulation.csv.gz myminio/mycsvbucket/sampledata/
+```
+
+Now let us proceed to run our select example to query for `Location` which matches `United States`.
+```sh
+$ python3 select.py
+840,United States of America,2,Medium,1950,1950.5,79233.218,79571.179,158804.395
+
+840,United States of America,2,Medium,1951,1951.5,80178.933,80726.116,160905.035
+
+840,United States of America,2,Medium,1952,1952.5,81305.206,82019.632,163324.851
+
+840,United States of America,2,Medium,1953,1953.5,82565.875,83422.307,165988.190
+....
+....
+....
+
+Stats details bytesScanned:
+6758866
+Stats details bytesProcessed:
+25786743
+```
+
+## 5. Explore Further
+- [Use `mc` with Minio Server](https://docs.minio.io/docs/minio-client-quickstart-guide)
+- [Use `minio-go` SDK with Minio Server](https://docs.minio.io/docs/golang-client-quickstart-guide)
+- [Use `aws-cli` with Minio Server](https://docs.minio.io/docs/aws-cli-with-minio)
+- [Use `s3cmd` with Minio Server](https://docs.minio.io/docs/s3cmd-with-minio)
+- [The Minio documentation website](https://docs.minio.io)

docs/select/select.py

@@ -0,0 +1,33 @@
+#!/usr/bin/env/env python3
+import boto3
+
+s3 = boto3.client('s3',
+                  endpoint_url='http://localhost:9000',
+                  aws_access_key_id='minio',
+                  aws_secret_access_key='minio123',
+                  region_name='us-east-1')
+
+r = s3.select_object_content(
+    Bucket='mycsvbucket',
+    Key='sampledata/TotalPopulation.csv.gz',
+    ExpressionType='SQL',
+    Expression="select * from s3object s where s.Location like '%United States%'",
+    InputSerialization={
+        'CSV': {
+            "FileHeaderInfo": "USE",
+        },
+        'CompressionType': 'GZIP',
+    },
+    OutputSerialization={'CSV': {}},
+)
+
+for event in r['Payload']:
+    if 'Records' in event:
+        records = event['Records']['Payload'].decode('utf-8')
+        print(records)
+    elif 'Stats' in event:
+        statsDetails = event['Stats']['Details']
+        print("Stats details bytesScanned: ")
+        print(statsDetails['BytesScanned'])
+        print("Stats details bytesProcessed: ")
+        print(statsDetails['BytesProcessed'])

pkg/s3select/helpers.go

@@ -25,6 +25,9 @@ import (
 	"github.com/xwb1989/sqlparser"
 )
 
+// MaxExpressionLength - 256KiB
+const MaxExpressionLength = 256 * 1024
+
 // This function processes size so that we can calculate bytes BytesProcessed.
 func processSize(myrecord []string) int64 {
 	if len(myrecord) > 0 {