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[SPARK-18826][SS] Add 'latestFirst' option to FileStreamSource
Shixiong Zhu authored 
## What changes were proposed in this pull request?

When starting a stream with a lot of backfill and maxFilesPerTrigger, the user could often want to start with most recent files first. This would let you keep low latency for recent data and slowly backfill historical data.

This PR adds a new option `latestFirst` to control this behavior. When it's true, `FileStreamSource` will sort the files by the modified time from latest to oldest, and take the first `maxFilesPerTrigger` files as a new batch.

## How was this patch tested?

The added test.

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #16251 from zsxwing/newest-first.
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catalyst
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hive-thriftserver
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README.md
README.md

Spark SQL

This module provides support for executing relational queries expressed in either SQL or the DataFrame/Dataset API.

Spark SQL is broken up into four subprojects:

  • Catalyst (sql/catalyst) - An implementation-agnostic framework for manipulating trees of relational operators and expressions.
  • Execution (sql/core) - A query planner / execution engine for translating Catalyst's logical query plans into Spark RDDs. This component also includes a new public interface, SQLContext, that allows users to execute SQL or LINQ statements against existing RDDs and Parquet files.
  • Hive Support (sql/hive) - Includes an extension of SQLContext called HiveContext that allows users to write queries using a subset of HiveQL and access data from a Hive Metastore using Hive SerDes. There are also wrappers that allows users to run queries that include Hive UDFs, UDAFs, and UDTFs.
  • HiveServer and CLI support (sql/hive-thriftserver) - Includes support for the SQL CLI (bin/spark-sql) and a HiveServer2 (for JDBC/ODBC) compatible server.