LMDB 1.0 released with a breaking on-disk format change

Category: Infrastructure
Status: confirmed
Sources: upgrade notes, documentation, HN discussion
Summary: LMDB (Lightning Memory-Mapped Database), the embedded copy-on-write key-value store used by OpenLDAP, Monero, and many language bindings, tagged 1.0.0 on 2026-06-30, its first 1.0 after more than a decade on the 0.9.x line. The 1.0 on-disk format is incompatible with 0.9 and there is no in-place upgrade, so existing data must be exported with the 0.9 mdb_dump and reimported with the 1.0 mdb_load. New features listed in the upgrade notes are incremental backup, page-level checksums and encryption, databases on raw block devices, two-phase commit, and page sizes up to 64KB.
Comments: HN commenters report production caveats: write latency degrading into multi-hour stalls once a database grows to several hundred GB, and iOS not paging dirty mmap pages back to disk causing app OOM under churn; some moved to libmdbx or RocksDB. Several flagged the 0.9-to-1.0 dump-and-restore requirement as the main migration cost.
Why it matters: Operators running LMDB-backed systems must plan an explicit data migration to adopt 1.0, and the added checksums, encryption, and incremental backup change the durability and operational story for embedded deployments.
Follow-up: Track 1.0.x point releases, downstream adoption in OpenLDAP and the language bindings, and whether the reported large-database write-stall behavior persists in 1.0.