Re: LMDB data corruption/alignment issues on ARM

[Martin Lucina <martin@lucina.net>]

hyc@symas.com said:
> >My question is: Given that I'm storing C structs directly in LMDB, I need
> >to get at least word-aligned pointers back from LMDB in order to be able to
> >access the data safely.
> >
> >I've not found anything in the documentation or the source about being able
> >to tweak alignment of key and data values; I *think* that all I need is an
> >option where LMDB would guarantee a minimum word (4 byte in this case)
> >alignment of data.
> >
> >How hard would this be to implement? Would you consider such a feature?
> 
> LMDB guarantees 2-byte alignment of keys, and data is generally
> stored contiguously with keys. If you want 4-byte alignment, it's
> your responsibility to pad your keys to 4-byte boundaries. If you
> pad appropriately, your alignment will be preserved.

In this case the keys are size_t (4 bytes on the target) and I'm using
MDB_INTEGERKEY. I'm not sure what you mean by padding the keys to 4-byte
boundaries given that LMDB copies my data into its memory map and I have no
control over where it gets placed.

Martin