Matlab LMDB

Matlab LMDB wrapper for UNIX environment.

• See LMDB website.
• The implementation is based on mexplus.

See also matlab-leveldb.

The package does not contain any data serialization. Use char for storing keys and values. You will need to serialize any Matlab variables to directly save in the database. For example, using num2str and str2double. There are different serialization options, such as this serialization package or JSON format. Those using Caffe might want to use a Datum converter in the caffe-extension branch.

Build

Specify the MATLABDIR path.

make MATLABDIR=/usr/local/MATLAB/R2015a
make test

Edit Makefile to customize the build process.

In the caffe-extension branch, also specify the path to caffe.

make MATLABDIR=/usr/local/MATLAB/R2015a CAFFEDIR=../caffe

Example

% Open and close.
database = lmdb.DB('./db', 'MAPSIZE', 1024^3);
clear database;
readonly_database = lmdb.DB('./db', 'RDONLY', true, 'NOLOCK', true);
clear readonly_database;

% Read and write.
database.put('key1', 'value1');
database.put('key2', 'value2');
value1 = database.get('key1');
database.remove('key1');

% Iterator.
database.each(@(key, value) disp([key, ': ', value]));
count = database.reduce(@(key, value, count) count + 1, 0);

% Cursor.
cursor = database.cursor('RDONLY', true);
while cursor.next()
  key = cursor.key;
  value = cursor.value;
end
clear cursor;

% Transaction.
transaction = database.begin();
try
  transaction.put('key1', 'value1');
  transaction.put('key2', 'value2');
  transaction.commit();
catch exception
  transaction.abort();
end
clear transaction;

% Dump.
keys = database.keys();
values = database.values();

See help documentation of each function, or visit LMDB documentation to understand the flags.

Caffe extension

The caffe-extension branch includes utilities to convert Datum protocol buffer.

% Make plain datum.
image = imread('peppers.png');
label = 1;
datum = caffe_pb.toDatum(image, label);

% Make encoded datum.
fid = fopen('peppers.png', 'r');
png_image = fread(fid, inf, 'uint8=>uint8');
fclose(fid);
label = 1;
datum = caffe_pb.toEncodedDatum(png_image, label);

% Read datum.
[png_image, label] = caffe_pb.fromDatum(datum);

TODO

• Finer transaction API.