[HUDI-9469] Improve performance for getting hoodie record / record ke…

[cshuo]

…y iterator for FG reader

Currently, getClosableHoodieRecordIterator has redundant conversion: engine record <->BufferedRecord, and getClosableKeyIterator has redundant process readerContext.getRecordKey. We actually can make a refactor to get these iterators more efficiently.

Change Logs

• Make the iterator element type for HoodieFileGroupReader generic.
• Introduce IteratorMode to HoodieFileGroupReader, which indicates what iterator the FileGroup reader will be return.

Impact

Improve performance for getting hoodie record / record key iterator for FG reader

Risk level (write none, low medium or high below)

low

Documentation Update

Describe any necessary documentation update if there is any new feature, config, or user-facing change. If not, put "none".

• The config description must be updated if new configs are added or the default value of the configs are changed
• Any new feature or user-facing change requires updating the Hudi website. Please create a Jira ticket, attach the ticket number here and follow the instruction to make changes to the website.

Contributor's checklist

• [ ] Read through contributor's guide
• [ ] Change Logs and Impact were stated clearly
• [ ] Adequate tests were added if applicable
• [ ] CI passed

[hudi-bot]

CI report:

• 19bba1a9222b5476d4be6c53bcc61af7ef562ab4 Azure: FAILURE

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