Add lsm tree support

[manishym]

No description provided.

[github-actions]

✅ Unit tests passed.

📊 Coverage Summary:

src/storage/stdmap_memtable.h             | 100%      2| 0.0%     2|    -      0
src/utils/file_buffer_writer.cpp          |50.0%     16| 0.0%     7|    -      0
src/utils/i_writable_buffer.h             | 200%      1| 0.0%     1|    -      0
src/wal/block_device_wal.h                |21.8%     55| 0.0%     8|    -      0
src/wal/interface.h                       | 200%      1| 0.0%     1|    -      0
src/wal/passthrough_wal.h                 | 100%      7| 0.0%     7|    -      0
src/wal/wal_entry_serializer.h            |12.1%     33| 0.0%     4|    -      0
src/wal/wal_factory.h                     | 7.1%     14| 0.0%     1|    -      0
src/wal/wal_serializer.cpp                |15.4%     13| 0.0%     1|    -      0
tests/unit/block_device_wal_test.cpp      |18.5%     65| 0.0%    12|    -      0
tests/unit/block_lsm_tree_test.cpp        |21.1%     19| 0.0%     4|    -      0
tests/unit/file_buffer_writer_test.cpp    |50.8%     59| 0.0%    30|    -      0
tests/unit/map_test.cpp                   |31.1%    132| 0.0%    41|    -      0
tests/unit/memtable_test.cpp              |33.3%     36| 0.0%    12|    -      0
tests/unit/passthrough_wal_test.cpp       |84.8%     33| 0.0%    28|    -      0
tests/unit/server_test.cpp                |21.6%     37| 0.0%     8|    -      0
tests/unit/wal_factory_test.cpp           |70.6%     17| 0.0%    12|    -      0
tests/unit/wal_serializer_test.cpp        |49.3%     73| 0.0%    36|    -      0
================================================================================
                                    Total:|32.8%    892| 0.0%   273|    -      0

[Copilot]

Pull Request Overview

This PR introduces LSM Tree support to the key-value store system. The implementation provides a block-based LSM Tree structure with automatic memtable flushing to persistent SST files on disk when size thresholds are reached.

• Adds BlockLSMTree class with put/get/delete operations and automatic memtable flushing
• Implements SST file persistence using WAL entry serialization format
• Integrates LSM configuration into the runtime configuration system

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/storage/block_lsm_tree.h	Defines the BlockLSMTree class interface with memtable and SST file management
src/storage/block_lsm_tree.cpp	Implements LSM tree operations, memtable flushing, and SST file search functionality
tests/unit/block_lsm_tree_test.cpp	Adds unit test for flush-on-threshold behavior and file verification
src/config/runtime_config.json	Adds LSM configuration section with memtable size and directory settings
CMakeLists.txt	Integrates new source and test files into build system

Comments suppressed due to low confidence (1)

tests/unit/block_lsm_tree_test.cpp:21

• Test does not verify cleanup failure scenarios. If rmdir or std::remove fail, subsequent test runs may be affected by leftover files.

    ASSERT_EQ(stat("lsm_test/sst_0.sst", &st), 0);

[Copilot]

File descriptor is not checked for error before use. If open() fails, fd will be negative but the code continues to use it in subsequent operations.

Suggested change

	if (fd < 0)
	return;
	if (fd < 0) {
	std::cerr << "Error opening file '" << path << "': " << std::strerror(errno) << std::endl;
	return;
	}

[Copilot]

Early return on file open failure leaves the SST file path untracked, but memtable data is lost. This could cause data loss as the memtable should only be cleared after successful flush.

[Copilot]

When writeAll fails, the function breaks out of the loop but still adds the partially written file to sst_files_ and clears the memtable, potentially causing data loss.

[Copilot]

No validation of klen and vlen values read from file. Malformed or malicious SST files could cause excessive memory allocation or integer overflow.

Suggested change

	std::memcpy(&vlen, header+1+sizeof(uint32_t), sizeof(uint32_t));
	std::memcpy(&vlen, header+1+sizeof(uint32_t), sizeof(uint32_t));
	if (klen > MAX_KEY_LENGTH || vlen > MAX_VALUE_LENGTH) {
	::close(fd);
	return false;
	}

[Copilot]

[nitpick] Magic number for header size calculation. Consider defining a constant like HEADER_SIZE to make the code more readable and maintainable.

Suggested change

	uint8_t header[1 + sizeof(uint32_t)*2];
	ssize_t r = ::read(fd, header, sizeof(header));
	uint8_t header[HEADER_SIZE];
	ssize_t r = ::read(fd, header, HEADER_SIZE);