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Re: dbm_store() returns -1, but no specific error is reported



On Nov 28, 2007, at 10:45 AM, Christian Moen wrote:

darwin-dev,

I'm experiencing strange behaviour with DBM on a Mac OS X 10.5.1 (both
on G5 and Intel) and it would be great to get some feedback from the
list on what the problem might be.

Running a quick dtrace script (attached) reveals that this fails due to an overflow page not being added:

  1            <- memcmp                          10001
  1            -> __addel                          1788
  1              -> __add_ovflpage                 1789
  1              <- __add_ovflpage                 7068
  1            <- __addel                          7067
  1          <- hash_access                        7005
  1        <- dbm_store                            7896

So __add_ovflpage is failing. But I'm not sure which source this is built
from. I thought it was the BerkeleyDB-15 package, but that doesn't seem
to have this function (it has __ham_add_ovflpage instead)...ah, we're
working with LibC-548 instead. [Is the BerkeleyDB code shipped somehow?]


So, looking at

  http://www.opensource.apple.com/darwinsource/10.5/Libc-498/db/hash/hash_page-fbsd.c

it appears that overflow_page() must be returning 0, indicating that there
are no usable free pages in the database file. There are some strange (to
my eye) limits on which pages can be used for overflow pages.


This looks like pretty old DBM code. I'm not sure I'd rely on it for larger
databases. You could probably use the btree instead of hash code (using the
dbopen interface) and at least get a larger file. But I'd still wonder if
Apple's shipping a more up-to-date database somewhere....


-- Anton

Attachment: test.d
Description: Binary data


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References: 
 >dbm_store() returns -1, but no specific error is reported (From: "Christian Moen" <email@hidden>)



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