[ENGINE] Added wal api to Heap File + refactored heap file into several files

[kTrzcinskii]

Main files that should be checked in PR:

• lock_chains.rs and mod.rs, others are just moving code from one place to another

[Copilot]

Pull request overview

This pull request refactors the heap file module into multiple files and adds WAL (Write-Ahead Logging) API support for atomic multi-page operations. The main changes include:

• Introduction of lock chain abstractions to manage page locking patterns
• Addition of PageCollector trait to gather modified pages for batch WAL logging
• Refactoring of heap file code into separate modules (error, fsm, lock_chains, pages, record)

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
engine/src/heap_file/lock_chains.rs	New file introducing lock chain traits and implementations for managing page locking patterns with WAL support
engine/src/heap_file/mod.rs	Major refactoring to use new lock chains and PageCollector; methods updated to support multi-page WAL operations
engine/src/heap_file/record.rs	Moved record-related types (RecordPtr, RecordTag, RecordFragment, RecordHandle) from mod.rs
engine/src/heap_file/pages.rs	Moved page-related types (Metadata, page headers, HeapPage) from mod.rs
engine/src/heap_file/error.rs	Extracted HeapFileError enum into separate error module
engine/src/heap_file/fsm.rs	Moved FreeSpaceMap implementation from mod.rs to dedicated module
executor/src/statement_executor.rs	Updated imports to reflect new module structure
executor/src/error_factory.rs	Updated imports to reflect new module structure
engine/src/b_tree_node.rs	Updated imports to reflect new module structure
engine/src/b_tree.rs	Updated imports to reflect new module structure
engine/src/lib.rs	Removed extra blank line

Comments suppressed due to low confidence (5)

engine/src/heap_file/mod.rs:230

• The insert method only calls drop_pages if result.is_ok(), which means if an error occurs during insertion, the pages collected in the InsertPageLockChain are never dropped via drop_write_pages. These pinned write pages will be dropped individually when page_chain goes out of scope, but this may leak the pages or fail to properly notify the WAL system. Consider calling drop_pages unconditionally, or at minimum in an error case as well to ensure proper resource cleanup.
  engine/src/heap_file/mod.rs:260
• The update operation creates an ExclusivePageLockChain but never calls drop_pages on it. Unlike the insert method which explicitly calls drop_pages, this method relies on Drop trait behavior which ExclusivePageLockChain does not implement. This means the pages held by the lock chain will be dropped individually instead of as a multi-page WAL operation, which breaks the intended atomicity guarantee for WAL logging. The fix is to either call page_chain.drop_pages() explicitly at the end of this method, or implement Drop trait for ExclusivePageLockChain to automatically call drop_pages.
  engine/src/heap_file/mod.rs:277
• The delete operation creates an ExclusivePageLockChain but never calls drop_pages on it. Like the update method, this means pages will be dropped individually rather than as a multi-page WAL operation, breaking atomicity. This needs to either call page_chain.drop_pages() explicitly or rely on a Drop trait implementation.
  engine/src/heap_file/mod.rs:340
• The add_column_migration creates a NoDroppingPageLockChain which accumulates pages throughout the entire operation but never calls drop_pages at the end. This means all the modified pages during the migration will be dropped individually rather than as a single multi-page WAL operation. This is particularly critical for schema migrations which should be atomic. The fix is to add chain.drop_pages() after the while loop completes successfully (line 339).
  engine/src/heap_file/mod.rs:378
• The remove_column_migration creates a NoDroppingPageLockChain which accumulates pages throughout the entire operation but never calls drop_pages at the end. Like add_column_migration, this means all modified pages will be dropped individually instead of as a single multi-page WAL operation, breaking atomicity for schema migrations. The fix is to add chain.drop_pages() after the while loop completes successfully (line 378).

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