#15 persistent object storage
if I want to save a data structure,
I have two options now:
1. WRITE to a file
2. SAVEINITMEM
both have drawbacks:
1. WRITE uses ascii text which may be slow to
read and write, and it may fail for large
highly circular data because of STACK.
2. MEM cannot be loaded at will: if I want to run
something on 3 datasets, I must start 3 processes.
I suggest that we add object save/retrieve facility
with a berklely-db backend -
probably in the BDB module.
HASH Berkely-DB tables appear to be the right choice.
pointer objects are to be written as records keyed on
as_oint(obj) and with value being the memory to which
the object pointer refers, with other pointer objects
replaced
with as_oint(obj).
immediate slot values are to be written as is.
challenges:
1. thus must be platform-independent
(including 64-bit vs 32-bit).
2. will this require me to write a separate routine
for every single CLISP built-in type?
Comments?
Suggestions?
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note also that MEM files are extremely platform-dependent,
so they are next to useless for data storage.
WRITE is good because it lets one edit data with a text editor.
unfortunately, to get linebreaks there requires *print-pretty*
set to T, which makes output VERY slot (remember, we
are talking about HUGE data piles) and without any linebreaks
even emacs edits huge files VERY slowly.
a DB-based storage will let one edit the data "programmatically"
before loading the whole thing.
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<http://article.gmane.org/gmane.lisp.clisp.devel:12214>
<http://article.gmane.org/gmane.lisp.clisp.devel:12225>
<http://article.gmane.org/gmane.lisp.clisp.devel:12226>
<http://sourceforge.net/mailarchive/message.php?msg_id=9137008>
<http://sourceforge.net/mailarchive/message.php?msg_id=9139407>
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<http://www.common-lisp.net/project/elephant/>
an object database for common lisp
no code released yet.
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<http://common-lisp.net/project/cl-store/>
A Common Lisp Serialization Package
writes binary to streams, can probably be adapted
for database purposes.
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<http://lecture.pentaside.org/paper/persistence-lemmens.txt>
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different backends should be permitted - streams as well as BDB.