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partial file locking with ndbm(3) files

partial file locking with ndbm(3) files

Post by Steve Be » Wed, 02 May 1990 22:28:00



  I'm trying to write a database application (a small one) which
uses ndbm(3).  I'd like to find out how I could write my application
so that a minimum portion of the database is locked at any one
time.  Naturally, the ndbm man page skirts the whole issue of record
locking (What is a concurrent update anyway? :-)

  The most common operations on the database will be (in this order):

   search every record for some trait or another.
   update a single record.
   add a single record.

  I'd rather not lock the whole database when I do a 'search' since
that might hold up the updates&adds for an inordinate amount of time.
While I can readily see how to accomplish a whole-database locking
scheme, I think my performance would be substantially better with
single-record locking.

                                - Steve Benz
                                ...!hubcap!mrspock

 
 
 
Top

1. ndbm and file locking

I have an ndbm database which could be accessed by more than one
process at a time.  So, of course I want to do file locking.

So I have a few questions which should be vendor independent (I hope).

lockf wants a file descriptor for the first argument, not a pointer to
DBM.

So,

1) Should I open the .pag file RDWR, do a lock on it, and then in
   the same process, do the dbm_open, dbm_store, dbm_close?

2) I would think I'll have to lock the entire file, as that fd isn't
   going to know what offset in the file will point to where
   I am about to write in the .pag file.  Must I lock the entire
   file?

As I said, this would seem to be vendor independent, but I'll mention
that I am running Solaris 2.3+patches on a Sparc 20.

Thanks in advance for any ideas/suggestions/comments.

-rob
---
Rob Francis
Paradigm Systems   <URL:http://www.sf.psca.com/Hyplans/rfrancis/>

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