# Advanced options
Advanced

## Fetch size


The maximum number of results (rows) to return in this request. For parameter information, see [GetQuery MaxResults](https://docs.aws.amazon.com/athena/latest/APIReference/API_GetQueryResults.html#athena-GetQueryResults-request-MaxResults). For the streaming API, the maximum value is 10000000.


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
| RowsToFetchPerBlock | Optional |  `1000` for non-streaming `20000` for streaming  | RowsToFetchPerBlock=20000; | 

## Result fetcher


The default result fetcher downloads query results directly from Amazon S3 without going through the Athena API operations. When it detects situations where direct S3 download is not possible, it automatically falls back to using the `GetQueryResultsStream` API operation. For example, this happens when query results are encrypted with the `CSE_KMS` option. 

Using the `auto` fetcher is recommended in most situations. However, if your IAM policies, or S3 bucket policies use the `s3:CalledVia` condition to limit access to S3 objects to requests from Athena, the auto fetcher first attempts to download the results from S3 and then falls back to using the `GetQueryResultsStream`. In this situation, you might want to set the `ResultFetcher` to `GetQueryResultsStream` to avoid an extra API call.

**Note**  
The driver still recognizes the Enable streaming API (`UseResultsetStreaming=1;`) and Enable S3 fetcher (`EnableS3Fetcher=1;`) parameters. However, we encourage you to use `ResultFetcher` parameter for better experience.


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| **Connection string name** | **Parameter type** | **Default value** | **Possible values** | **Connection string example** | 
| --- | --- | --- | --- | --- | 
|  ResultFetcher  | Optional | auto | auto, S3, GetQueryResults, GetQueryResultsStream | ResultFetcher=auto | 

## Enable result reuse


Specifies if previous query results can be reused when the query is run. For parameter information, see ResultReuseByAgeConfiguration.


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
| EnableResultReuse | Optional | 0 | EnableResultReuse=1; | 

## Result reuse maximum age


Specifies, in minutes, the maximum age of a previous query result that Athena should consider for reuse. For parameter information, see [ResultReuseByAgeConfiguration](https://docs.aws.amazon.com/athena/latest/APIReference/API_ResultReuseByAgeConfiguration.html).


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
| ReusedResultMaxAgeInMinutes | Optional | 60 | ReusedResultMaxAgeInMinutes=90; | 

## Use multiple S3 threads


Fetches data from Amazon S3 using multiple threads. When this option is enabled, the result file stored in the Amazon S3 bucket is fetched in parallel using multiple threads.

Enable this option only if you have good network bandwidth. For example, in our measurements on an EC2 [c5.2xlarge](https://aws.amazon.com/ec2/instance-types/c5/) instance, a single-threaded S3 client reached 1 Gbps, while multiple-threaded S3 clients reached 4 Gbps of network throughput.


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
|  UseMultipleS3Threads  | Optional | 0 | UseMultipleS3Threads=1; | 

## Use single catalog and schema


By default, the ODBC driver queries Athena to get the list of available catalogs and schemas. This option forces the driver to use the catalog and schema specified by the ODBC Data Source Administrator configuration dialog box or connection parameters. 


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
| UseSingleCatalogAndSchema | Optional | 0 | UseSingleCatalogAndSchema=1; | 

## Use query to list tables


For `LAMBDA` catalog types, enables the ODBC driver to submit a [SHOW TABLES](show-tables.md) query to get a list of available tables. This setting is the default. If this parameter is set to 0, the ODBC driver uses the Athena [ListTableMetadata](https://docs.aws.amazon.com/athena/latest/APIReference/API_ListTableMetadata.html) API to get a list of available tables. Note that, for `LAMBDA` catalog types, using `ListTableMetadata` leads to performance regression. 


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
| UseQueryToListTables | Optional | 1 | UseQueryToListTables=1; | 

## Use WCHAR for string types


By default, the ODBC driver uses `SQL_CHAR` and `SQL_VARCHAR` for Athena the string data types `char`, `varchar`, `string`, `array`, `map<>`, `struct<>`, and `row`. Setting this parameter to `1` forces the driver to use `SQL_WCHAR` and `SQL_WVARCHAR` for string data types. Wide character and wide variable character types are used to ensure that characters from different languages can be stored and retrieved correctly.


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
| UseWCharForStringTypes | Optional | 0 | UseWCharForStringTypes=1; | 

## Query external catalogs


Specifies if the driver needs to query external catalogs from Athena. For more information, see [Migrate to the ODBC 2.x driver](odbc-v2-driver-migrating.md).


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
| QueryExternalCatalogs | Optional | 0 | QueryExternalCatalogs=1; | 

## Verify SSL


Controls whether to verify SSL certificates when you use the AWS SDK. This value is passed to `ClientConfiguration.verifySSL` parameter. For more information, see [AWS Client configuration](https://docs.aws.amazon.com/sdk-for-cpp/v1/developer-guide/client-config.html) in the *AWS SDK for C\$1\$1 Developer Guide*.


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
| VerifySSL | Optional | 1 | VerifySSL=0; | 

## S3 result block size


Specifies, in bytes, the size of the block to download for a single Amazon S3 [GetObject](https://docs.aws.amazon.com/AmazonS3/latest/API/API_GetObject.html) API request. The default value is 67108864 (64 MB). The minimum and maximum values allowed are 10485760 (10 MB) and 2146435072 (about 2 GB). 


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
| S3ResultBlockSize | Optional | 67108864 | S3ResultBlockSize=268435456; | 

## String column length


Specifies the column length for columns with the `string` data type. Because Athena uses the [Apache Hive string data type](https://cwiki.apache.org/confluence/display/Hive/LanguageManual+Types#LanguageManualTypes-StringsstringStrings), which does not have defined precision, the default length reported by Athena is 2147483647 (`INT_MAX`). Because BI tools usually pre-allocate memory for columns, this can lead to high memory consumption. To avoid this, the Athena ODBC driver limits the reported precision for columns of the `string` data type and exposes the `StringColumnLength` connection parameter so that the default value can be changed.


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| Connection string name | Parameter type | Default value | Connection string example | 
| --- | --- | --- | --- | 
| StringColumnLength | Optional | 255 | StringColumnLength=65535; | 

## Complex type column length


Specifies the column length for columns with complex data types like `map`, `struct`, and `array`. Like [StringColumnLength](#odbc-v2-driver-advanced-options-string-column-length), Athena reports 0 precision for columns with complex data types. The Athena ODBC driver sets the default precision for columns with complex data types and exposes the `ComplexTypeColumnLength` connection parameter so that the default value can be changed.


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| Connection string name | Parameter type | Default value | Connection string example | 
| --- | --- | --- | --- | 
| ComplexTypeColumnLength | Optional | 65535 | ComplexTypeColumnLength=123456; | 

## Trusted CA certificate


Instructs the HTTP client where to find your SSL certificate trust store. This value is passed to the `ClientConfiguration.caFile` parameter. For more information, see [AWS Client configuration](https://docs.aws.amazon.com/sdk-for-cpp/v1/developer-guide/client-config.html) in the *AWS SDK for C\$1\$1 Developer Guide*.


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
| TrustedCerts | Optional | %INSTALL\$1PATH%/bin | TrustedCerts=C:\$1\$1Program Files\$1\$1Amazon Athena ODBC Driver\$1\$1bin\$1\$1cacert.pem; | 

## Min poll period


Specifies the minimum value in milliseconds to wait before polling Athena for query execution status.


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
| MinQueryExecutionPollingInterval | Optional | 100 | MinQueryExecutionPollingInterval=200; | 

## Max poll period


Specifies the maximum value in milliseconds to wait before polling Athena for the query execution status.


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
| MaxQueryExecutionPollingInterval | Optional | 60000 | MaxQueryExecutionPollingInterval=1000; | 

## Poll multiplier


Specifies the factor for increasing the poll period. By default, polling begins with the value of min poll period and doubles with each poll until it reaches the value of max poll period.


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
| QueryExecutionPollingIntervalMultiplier | Optional | 2 | QueryExecutionPollingIntervalMultiplier=2; | 

## Max poll duration


Specifies the maximum value in milliseconds that a driver can poll Athena for query execution status.


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
| MaxPollDuration | Optional | 1800000 | MaxPollDuration=1800000; | 

## Connection timeout


The amount of time (in milliseconds) that the HTTP connection waits to establish a connection. This value is set for `ClientConfiguration.connectTimeoutMs` Athena client. If not specified, the curl default value is used. For information about connection parameters, see [Client Configuration](https://docs.aws.amazon.com/sdk-for-java/v1/developer-guide/section-client-configuration.html) in the *AWS SDK for Java Developer Guide*.


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
| ConnectionTimeout | Optional | 0 | ConnectionTimeout=2000; | 

## Request timeout


Specifies the socket read timeout for HTTP clients. This value is set for the `ClientConfiguration.requestTimeoutMs` parameter of the Athena client. For parameter information, see [Client Configuration](https://docs.aws.amazon.com/sdk-for-java/v1/developer-guide/section-client-configuration.html) in the *AWS SDK for Java Developer Guide*.


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| **Connection string name** | **Parameter type** | **Default value** | **Connection string example** | 
| --- | --- | --- | --- | 
| RequestTimeout | Optional | 10000 | RequestTimeout=30000; |