Question 1

How does LMDB JNI compare to RocksDB for Java performance?

Accepted Answer

LMDB JNI often outperforms RocksDB in read-heavy scenarios due to its memory-mapped architecture; benchmarks show zero-copy scans at 16M ops/sec vs 1.3M for RocksDB. However, RocksDB may handle write-intensive loads better with configurable LSM trees.

Question 2

How to use zero-copy mode in LMDB JNI for max speed?

Accepted Answer

Use the BufferCursor API within read or write transactions, ensuring proper closure to avoid SIGSEGV. It allows direct access to memory-mapped data without copying, but requires careful buffer management and is not available on Android.

Question 3

Why does LMDB JNI throw SIGSEGV errors with cursors?

Accepted Answer

SIGSEGV errors typically arise from unsafe cursor usage, such as failing to close cursors before write-transaction ends. Always follow safe patterns from the README, like using try-with-resources for read-only transactions.

Question 4

Is LMDB JNI still supported on Windows for new projects?

Accepted Answer

No, Windows support was discontinued after version 0.4.7; users must build the native library themselves or switch to alternatives like lmdbjava for active cross-platform maintenance.

Question 5

How to backup an LMDB database using LMDB JNI?

Accepted Answer

Call Env.copy() for atomic hot backups, which creates a consistent snapshot of the database files without stopping transactions. This leverages LMDB's built-in crash-proof design for reliable persistence.

Question 6

What's the difference between LMDB JNI and lmdbjava?

Accepted Answer

LMDB JNI is an older binding with discontinued platform support, while lmdbjava is a newer, actively maintained alternative with better cross-platform compatibility and a pure-Java fallback, making it more future-proof.

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