Re: (ITS#7789) Unreliable mdb_env_set_mapsize()

[h.b.furuseth@usit.uio.no]

Should have enclosed a test program.  Here:
   http://folk.uio.no/hbf/testsize.c
Output:
   process #0: open env
   process #1: open env
   process #0: write txn, mapsize 204800
   process #1: write txn, mapsize 40960
   process #2: open env, write txn, mapsize 40960
   process #3: open env, write txn, mapsize 204800


Summarizing a reply which got sent privately instead of to ITS:

On 2014-01-24 00:07, Howard Chu wrote:
> The doc says the caller of set_mapsize is required to make sure there
> are no active transactions when it is called. As such, X failed this
> requirement, and this sequence of events is explicitly unsupported.

No, I'm talking about X changing the mapsize when there is no txn,
then afterwards doing a write txn so the mapsize gets written.

> If Y doesn't start its write txn until after X finishes, then Y will
> see the new size.

It doesn't, that's the point.  Only txn_commit pays attention,
and it checks the size which existed in the wrong metapage.

Come to think of it, set_mapsize(); env_open(); txn begin/end
should do the same.  Y will either way not pay attention to
the new mapsize.

-- 
Hallvard