Howard Chu writes:

h.b.furuseth@usit.uio.no wrote:

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I'd call this two doc bugs:

Something should mention that once a page has been used, the file will never shrink below that page. (Can't quite say that the file never shrinks, since WRITEMAP and Windows will set it to exact re-configurable mapsize in some cases. If I remember correctly.)

You cannot shrink the mapsize below that last used page, and the last used page is a non-decreasing number.

Yes. Duh, that's already roughly stated under mdb_env_set_mapsize().

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mdb_env_copy() and mdb_env_copyfd() should document that

@node This call can trigger siginficant file size growth if run in parallel with write transactions, because it employs a read-only transaction. See long-lived transactions under Caveats.

I'll add this one though.

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I wonder that means these functions should have a flag parameter. For some databases, users might prefer a _write_ transaction while reading the DB, blocking writes while copying.

No one has ever wanted a hot-backup function that halts writes. You might as well not do a hot-backup at all.

Yes, nevermind about a mdb_env_copy() flag. An mdb_txn_begin timeout would make it a viable choice - but if that is implemented someday, those two behaviors together could go in an MDB_env flag.