### What changes were proposed in this pull request?
Currently, there is no migration section for PySpark, SparkCore and Structured Streaming.
It is difficult for users to know what to do when they upgrade.
This PR proposes to create create a "Migration Guide" tap at Spark documentation.
This page will contain migration guides for Spark SQL, PySpark, SparkR, MLlib, Structured Streaming and Core. Basically it is a refactoring.
There are some new information added, which I will leave a comment inlined for easier review.
1. **MLlib**
Merge [ml-guide.html#migration-guide](https://spark.apache.org/docs/latest/ml-guide.html#migration-guide) and [ml-migration-guides.html](https://spark.apache.org/docs/latest/ml-migration-guides.html)
```
'docs/ml-guide.md'
↓ Merge new/old migration guides
'docs/ml-migration-guide.md'
```
2. **PySpark**
Extract PySpark specific items from https://spark.apache.org/docs/latest/sql-migration-guide-upgrade.html
```
'docs/sql-migration-guide-upgrade.md'
↓ Extract PySpark specific items
'docs/pyspark-migration-guide.md'
```
3. **SparkR**
Move [sparkr.html#migration-guide](https://spark.apache.org/docs/latest/sparkr.html#migration-guide) into a separate file, and extract from [sql-migration-guide-upgrade.html](https://spark.apache.org/docs/latest/sql-migration-guide-upgrade.html)
```
'docs/sparkr.md' 'docs/sql-migration-guide-upgrade.md'
Move migration guide section ↘ ↙ Extract SparkR specific items
docs/sparkr-migration-guide.md
```
4. **Core**
Newly created at `'docs/core-migration-guide.md'`. I skimmed resolved JIRAs at 3.0.0 and found some items to note.
5. **Structured Streaming**
Newly created at `'docs/ss-migration-guide.md'`. I skimmed resolved JIRAs at 3.0.0 and found some items to note.
6. **SQL**
Merged [sql-migration-guide-upgrade.html](https://spark.apache.org/docs/latest/sql-migration-guide-upgrade.html) and [sql-migration-guide-hive-compatibility.html](https://spark.apache.org/docs/latest/sql-migration-guide-hive-compatibility.html)
```
'docs/sql-migration-guide-hive-compatibility.md' 'docs/sql-migration-guide-upgrade.md'
Move Hive compatibility section ↘ ↙ Left over after filtering PySpark and SparkR items
'docs/sql-migration-guide.md'
```
### Why are the changes needed?
In order for users in production to effectively migrate to higher versions, and detect behaviour or breaking changes before upgrading and/or migrating.
### Does this PR introduce any user-facing change?
Yes, this changes Spark's documentation at https://spark.apache.org/docs/latest/index.html.
### How was this patch tested?
Manually build the doc. This can be verified as below:
```bash
cd docs
SKIP_API=1 jekyll build
open _site/index.html
```
Closes#25757 from HyukjinKwon/migration-doc.
Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: Dongjoon Hyun <dhyun@apple.com>
## What changes were proposed in this pull request?
Add AL2 license to metadata of all .md files.
This seemed to be the tidiest way as it will get ignored by .md renderers and other tools. Attempts to write them as markdown comments revealed that there is no such standard thing.
## How was this patch tested?
Doc build
Closes#24243 from srowen/SPARK-26918.
Authored-by: Sean Owen <sean.owen@databricks.com>
Signed-off-by: Sean Owen <sean.owen@databricks.com>
## What changes were proposed in this pull request?
Fix a few broken links and typos, and, nit, use HTTPS more consistently esp. on scripts and Apache links
## How was this patch tested?
Doc build
Closes#22172 from srowen/DocTypo.
Authored-by: Sean Owen <sean.owen@databricks.com>
Signed-off-by: hyukjinkwon <gurwls223@apache.org>
## What changes were proposed in this pull request?
Easy fix in the documentation.
## How was this patch tested?
N/A
Closes#20948
Author: Daniel Sakuma <dsakuma@gmail.com>
Closes#20928 from dsakuma/fix_typo_configuration_docs.
Update ML user guide with highlights and migration guide for `2.3`.
## How was this patch tested?
Doc only.
Author: Nick Pentreath <nickp@za.ibm.com>
Closes#20363 from MLnick/SPARK-23112-ml-guide.
Update ML guide for migration `2.1` -> `2.2` and the previous version migration guide section.
## How was this patch tested?
Build doc locally.
Author: Nick Pentreath <nickp@za.ibm.com>
Closes#17996 from MLnick/SPARK-20506-2.2-migration-guide.
## What changes were proposed in this pull request?
Update ML programming and migration guide for 2.1 release.
## How was this patch tested?
Doc change, no test.
Author: Yanbo Liang <ybliang8@gmail.com>
Closes#16076 from yanboliang/spark-18324.
## What changes were proposed in this pull request?
Made DataFrame-based API primary
* Spark doc menu bar and other places now link to ml-guide.html, not mllib-guide.html
* mllib-guide.html keeps RDD-specific list of features, with a link at the top redirecting people to ml-guide.html
* ml-guide.html includes a "maintenance mode" announcement about the RDD-based API
* **Reviewers: please check this carefully**
* (minor) Titles for DF API no longer include "- spark.ml" suffix. Titles for RDD API have "- RDD-based API" suffix
* Moved migration guide to ml-guide from mllib-guide
* Also moved past guides from mllib-migration-guides to ml-migration-guides, with a redirect link on mllib-migration-guides
* **Reviewers**: I did not change any of the content of the migration guides.
Reorganized DataFrame-based guide:
* ml-guide.html mimics the old mllib-guide.html page in terms of content: overview, migration guide, etc.
* Moved Pipeline description into ml-pipeline.html and moved tuning into ml-tuning.html
* **Reviewers**: I did not change the content of these guides, except some intro text.
* Sidebar remains the same, but with pipeline and tuning sections added
Other:
* ml-classification-regression.html: Moved text about linear methods to new section in page
## How was this patch tested?
Generated docs locally
Author: Joseph K. Bradley <joseph@databricks.com>
Closes#14213 from jkbradley/ml-guide-2.0.
