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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Hello,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>I’m the product manager for Berkeley DB at
Oracle. CDS does allow multiple readers and a single writer, it
uses database level locking. It doesn’t provide protection from
failure or transactions and recovery. In other words, if your application
crashes you can’t expect the data in the database to be consistent.
For that you’ll need to use TDS (transactional data store). It
provides page level locking and ACID transactions. It ensures consistency
of the data even if you crash during database operations.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>You might take a minute (okay an hour) to watch these two
tutorial videos in order (first DS, then CDS, we’re working on TDS and HA
videos now).<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif"'><a
href="http://www.oracle.com/technology/products/berkeley-db/tutorial-berkeleydb-ds.html">http://www.oracle.com/technology/products/berkeley-db/tutorial-berkeleydb-ds.html</a><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif"'><a
href="http://www.oracle.com/technology/products/berkeley-db/tutorial-berkeleydb-cds.html">http://www.oracle.com/technology/products/berkeley-db/tutorial-berkeleydb-cds.html</a><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif"'>I
hope that helps.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif"'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>-greg<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Jeff Johnson
[mailto:jbj@jbj.org] <br>
<b>Sent:</b> Saturday, October 03, 2009 4:53 PM<br>
<b>To:</b> Python bindings for Oracle Berkeley DB<br>
<b>Subject:</b> Re: [pybsddb] concurrent access dictionaries<o:p></o:p></span></p>
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</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<div>
<div>
<p class=MsoNormal>On Oct 3, 2009, at 3:21 PM, Benjamin Rutt wrote:<o:p></o:p></p>
</div>
<p class=MsoNormal><br>
<br>
<o:p></o:p></p>
<p>The docs say (for the version shipped with python 2.6), in <a
href="http://www.jcea.es/programacion/pybsddb_doc/4.7.3/introduction.html#introduction">http://www.jcea.es/programacion/pybsddb_doc/4.7.3/introduction.html#introduction</a>:<br>
<br>
"3. Concurrent access dictionaries: This refers to the ability to
simultaneously have one writer and multiple readers of a DB (either in multiple
threads or processes) and is implemented simply by creating a DBEnv with
certain flags. No extra work is required to allow this access mode in
bsddb3."<br>
<br>
Could someone elaborate on exactly which "certain flags" are needed
when creating the DBEnv to achieve the goal here in #3? Did I get it
right below (for the b-tree access method)?<o:p></o:p></p>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<p class=MsoNormal>Sure.<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>This is the "INIT_CDB" model, been used by RPM for
years.<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>Disclaimer: I don't use pybsddb nor python, but I do use
Berkeley DB<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>with INIT_CDB daily for years.<o:p></o:p></p>
</div>
<div>
<blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'>
<p>from bsddb import db<br>
<br>
env = db.DBEnv()<br>
env.open('/some/dir', db.DB_CREATE | db.DB_THREAD | db.DB_INIT_CDB |
db.DB_INIT_MPOOL)<br>
dbh = db.DB(env)<br>
dbh.open("foo.db", None, db.DB_BTREE, db.DB_CREATE)<br>
<br clear=all>
<o:p></o:p></p>
</blockquote>
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<p class=MsoNormal><o:p> </o:p></p>
</div>
<p class=MsoNormal>These flags look right to me. Try w/o DB_THREAD if you need
a sanity check,<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>that's exactly what RPM uses. DB_THREAD is needed iff you
have threads<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>sharing the same locks as processes.<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>73 de Jeff<o:p></o:p></p>
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