Portability of binary data structures across environments is IMO irrelevant. We export to plaintext for migrations. Writing in a binary format that is portable

Portability of binary data structures across environments is IMO irrelevant. We export to plaintext for migrations. Writing in a binary format that is portable across both 32 and 64 bit CPU architectures will be a waste on one or the other of the archs, and the point of approaches like this is to optimize runtime performance. Your point about serialisation occurring with a known state is not lost in an mmap approach. If you have transactional writes (as LMDB does), then writing to the mmap also only occurs with a known state. In reality, e.g. in OpenLDAP, you wind up with a minimal serialisation step, but with zero deserialisation. E.g., if I want to store a record: typedef struct foo { int len; char *data; } foo; The struct and the data of the char ptr may originally have been obtained from two separate mallocs and thus reside at very different locations in memory. My serializer would simply allocate a new block and store the character data contiguously with the end of the struct. If you mmap at a fixed address, then you can store the address of the character data directly in the struct's "data" field, and the next time you come around to use this record, no deserialization is needed. Explicit deserialization is truly just a waste.