Getting the gem version working
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README.textile
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README.textile
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This interface is most closely based on the DB4 C api and tries to
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maintain close interface proximity.
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h1. Bdb
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That API is published by sleepycat at
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Ruby bindings for Berkeley DB versions 4.2-4.6.
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http://www.sleepycat.com/docs/api_c/frame.html
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h2. Download
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function all arguments that are systematically omitted are leading
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DB handles and TXN handles. A few calls omit the flags parameter when the
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documenation indicates that no flag values are used. cursor.close is one.
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Currently this library is available via git at:
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the defines generator is imperfect and includes some defines that are not
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flags. while it could be improved, it is easier to delete the incorrect ones.
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thus, if you decide to rebuild the defines, you will need to edit the resulting
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file. this may be necessary if using a different release of DB4 than the one
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I used.
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git://github.com/mattbauer/bdb.git
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I have put all possible caution into ensuring that DB and Ruby cooperate.
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The memory access was one apsect carefully considered. Since Ruby copies
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h2. Installation
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h3. From Git
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You can check out the latest source from git:
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> git clone git://github.com/mattbauer/bdb.git
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h3. As a Gem
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At the moment this library is not available on Rubyforge. To install it as a
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gem, do the following:
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> sudo env ARCHFLAGS="-arch i386" gem install mattbauer-bdb --source http://gems.github.com -- --with-db-dir=/usr/local/BerkeleyDB.4.7
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This assumes you're on OS X and BerkeleyDB wasn't compiled as a universal binary.
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h2. Sample Usage
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<pre>
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env = Bdb::Env.new(0)
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env_flags = Bdb::DB_CREATE | # Create the environment if it does not already exist.
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Bdb::DB_INIT_TXN | # Initialize transactions
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Bdb::DB_INIT_LOCK | # Initialize locking.
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Bdb::DB_INIT_LOG | # Initialize logging
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Bdb::DB_INIT_MPOOL # Initialize the in-memory cache.
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env.open(File.join(File.dirname(__FILE__), 'tmp'), env_flags, 0);
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db = env.db
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db.open(nil, 'db1.db', nil, Bdb::Db::BTREE, Bdb::DB_CREATE | Bdb::DB_AUTO_COMMIT, 0)
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txn = env.txn_begin(nil, 0)
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db.put(txn, 'key', 'value', 0)
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txn.commit(0)
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value = db.get(nil, 'key', nil, 0)
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db.close(0)
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env.close
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</pre>
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h2. API
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This interface is most closely based on the DB4 C api and tries to maintain close
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interface proximity. That API is published by Oracle at "http://www.oracle.com/technology/documentation/berkeley-db/db/api_c/frame.html":http://www.oracle.com/technology/documentation/berkeley-db/db/api_c/frame.html.
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All function arguments systematically omit the leading DB handles and TXN handles.
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A few calls omit the flags parameter when the documentation indicates that no
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flag values are used - cursor.close is one.
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h2. Notes
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The defines generator is imperfect and includes some defines that are not
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flags. While it could be improved, it is easier to delete the incorrect ones.
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Thus, if you decide to rebuild the defines, you will need to edit the resulting
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file. This may be necessary if using a different release of DB4 than the ones
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the authors developed against. In nearly every case the defines generator works
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flawlessly.
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The authors have put all possible caution into ensuring that DB and Ruby cooperate.
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The memory access was one aspect carefully considered. Since Ruby copies
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when doing String#new, all key/data retrieval from DB is done with a 0 flag,
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meaning that DB will be responsible. See the copied news group posting about
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the effect of that.
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meaning that DB will be responsible. See "this":http://groups.google.com/group/comp.databases.berkeley-db/browse_frm/thread/4f70a9999b64ce6a/c06b94692e3cbc41?tvc=1&q=dbt+malloc#c06b94692e3cbc41
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news group posting about the effect of that.
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The only other design consideration of consequence was associate. The prior
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version used a Ruby thread local variable and kept track of the current
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database in use. I decided to take a simpler approach since Ruby is green
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database in use. The authors decided to take a simpler approach since Ruby is green
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threads. A global array stores the VALUE of the Proc for a given association
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by the file descriptor number of the underlying database. This is looked
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up when the first layer callback is made. It would have been better considered
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if DB allowed the passing of a (void *) user data into the alloc that would
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be supplied during callback. So far this design has not produced any problems.
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[This is a message from comp.databases.berkeley-db]
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http://groups.google.com/group/comp.databases.berkeley-db/browse_frm/thread/4f70a9999b64ce6a/c06b94692e3cbc41?tvc=1&q=dbt+malloc#c06b94692e3cbc41
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Subject: Some questions about BerkeleyDB
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Patrick Schaaf
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Sep 16 2004, 9:31 am show options
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Hi Cylin,
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I'm only replying to one point; I'm not so sure about the others.
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>> >4.In http://www.sleepycat.com/docs/api_c/dbt_class.html#DB_DBT_MALLOC
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>I mean when we query by a key, and get return data( or key).
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>If we set DB_DBT_MALLOC or not ,what is the difference about
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>data.data/key.data?
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DB_DBT_MALLOC is only relevant for the DBT in which Berkeley DB
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gives you back data from the database.
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Without DB_DBT_MALLOC, i.e. with DBT.flags set to 0, after the successful
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query call, you will find in data.data a pointer into memory which is
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under the responsibility of Berkeley DB. It may be (I don't know for sure)
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a pointer into the memory mapped shared environment. You can copy from
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there to some place safe, and I think you must NOT assume that the pointer
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will be valid after another call to a retrieval function.
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On the other hand, when you set (before the retrieval call) that DBT's
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.flags field to DB_DBT_MALLOC, then the retrieval function of Berkeley DB
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will automatically call malloc() to get _new_ memory for the retrieved
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data, and you will find after the retrieval that data.data points
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to that memory. As it is newly malloc()ed, you can access it for as
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long as you want. IMPORTANT: it is also your responsibility to
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use free() when you don't need it any more.
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best regards
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Patrick
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22
bdb.gemspec
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bdb.gemspec
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@ -6,12 +6,26 @@ BDB_SPEC = Gem::Specification.new do |s|
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s.authors = ["Matt Bauer", "Dan Janowski"]
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s.email = "bauer@pedalbrain.com"
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s.summary = "A Ruby interface to BerkeleyDB"
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s.files = FileList['lib/**/*', 'ext/**/*', 'test/**/*', 'LICENSE', 'README.textile', 'Rakefile'].to_a
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s.files = ['bdb.gemspec',
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'ext/bdb.c',
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'ext/bdb.h',
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'ext/extconf.rb',
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'LICENSE',
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'README.textile',
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'Rakefile']
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s.test_files = ['test/cursor_test.rb',
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'test/db_test.rb',
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'test/env_test.rb',
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'test/stat_test.rb',
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'test/test_helper.rb',
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'test/txn_test.rb']
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s.extensions = ["ext/extconf.rb"]
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s.homepage = "http://github.com/mattbauer/bdb"
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s.require_paths = ["lib", "ext"]
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s.test_files = Dir.glob('test/*.rb')
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s.has_rdoc = true
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s.require_paths = ["lib", "ext"]
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s.test_files = Dir.glob('test/*.rb')
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s.has_rdoc = true
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s.rdoc_options = ["--main", "README.textile"]
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s.extra_rdoc_files = ["README.textile"]
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end
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