Re: [PLOB] Upcoming release 2.11

[Heiko K. <hei...@gm...>]

Moin Edi,

Edi Weitz schrieb:

>>I have still plans to replace PLOB's underlying library POSTORE with
>>Berkely DB, but unfortunately did not have the time to do so.
>>    
>>
>It'd be great if you could replace the underlying store with something
>else.  I wonder, however, if Berkeley DB is the right solution.
>Again, because of licensing (or rather pricing) issues.  See my email
>to the Elephant mailing list:
>
>  <http://common-lisp.net/pipermail/elephant-devel/2005-March/000121.html>
>  
>
Ok, reading this means that the Berkeley DB license is not suitable for 
Plob. Sigh.

>Could you describe in a few words which features have to be supported
>by an alternative back-end?
>
The requirements are not that high.

First, I know of a successor of POSTORE called `Lumberjack' with the 
same API. Unfortunately, it looks as if the work on Lumberjack has stuck 
a bit, since the author(s) told me that it is not yet ready for putting 
it into the public domain. I will ask them again.

Second, to me it looks as if  Plob should use its own underlying 
persistent heap. There are several options to this:

1. Abonding the mixed C-/LISP-approach of Plob, coding the persistent 
heap in LISP. Would mean a major redesign and cost a lot of effort.

2. Replace the POSTORE lib by an own implementation of a persistent 
heap, again in C. Would mean only a redesign on Plob's lower levels, 
with maybe moderate efforts. I cannot estimate what it would mean to 
replace the POSTORE lib by something coded in LISP, but I'm afraid that 
this would mean that I've to drop the idea of using Plob randomly in 
server or serverless mode and to decide on supporting only exactly one 
of these modes.

For option 2., the POSTORE API is not that complicated. There are 
functions for allocating a persistent record with a quite simple 
structure (references to other persistent  records and values [i.e., no 
references]), access functions to these records by their `object id', 
and some administrative functions like flushing, creating a new 
persistent heap etc. You find the interface in the SH_* functions 
declared in plob-2.10/src/include/postore.h. All other databasespecific 
stuff (transactions, btrees etc.) has been implemented in Plob anyway in 
the layer above the persistent heap.

Since my time for working on Plob is rather constrained, I would prefer 
option 2.

Viele Grüße from Hamburg, too,
Heiko

Heiko Kirschke
Achtern Barg 48
D-22885 Barsbüttel
Tel.: +49 40 225497