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Re: Avoiding read() of meta pages
Howard Chu writes:
> From: Howard Chu <email@example.com>
> To: Hallvard Breien Furuseth <firstname.lastname@example.org>,
> Subject: Re: Avoiding read() of meta pages
> Date: Tue, 15 Jan 2013 20:56:40 +0000
> Hallvard Breien Furuseth wrote:
>> I presume this can only be a problem when other processes have the
>> database open? In that situation, I think the read() can be avoided
>> by maintaining a copy of the relevant MDB_meta information in the
>> lock file. The read() only needs enough info to know how to map
>> the data file.
>> This would require a version increase for the lock file and programs
>> using it, but not for the database file.
> Since, as you note, the read only needs to see the map size, none of this work
> is necessary.
Why not? The mapsize can change. mdb_env_write_meta(): /* Persist any
increases of mapsize config */. It can also shrink during env_open, but
I think that was a mistake as written. Will get back to that later.