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Re: MDB v2: Replace meta pages with "meta position" word

I wrote:
> One thing about ACID - IIRC there are some potential data races which my
> single-word meta info in the header will fix.  E.g. if the user does ^Z
> at an unfortunate time, and with WRITEMAP updating the meta page while a
> txn is reading it.

Reproducible by sending frequent SIGSTOPs and SIGCONTs, with mdb.c
patched to verify (memcmp or checksum) the meta info after copying.
Happens even with 1 MDB process.

(Re comments elsewhere: Selecting a meta page is atomic, but
copying/writing it is not.)