chunked version of memcached

chunked-memcache-pseudocode.txt

// Wrap memcached to chunkify long values ("blobs").
// Write individual chunks using a key constructed from a unique GUID and chunk number.
// Store the GUID and the number of chunks as the value of the underlying key.
//
// We assume that memcached.read and memcached.write are asynchronous and return promises.
// We also define asynchonous assemble and disassemble routes.
//
// The behavior of this code is that when a key is read,
// even if another client starts writing a new value for the
// key, the previous value will be returned.

function makeChunkKey(guid, chunk_num) { return guid + '@' + chunk_num; }

function set(key, blob) {
  var guid = getGuid(), i = 0;
  return disassemble(blob) . 
    then(chunks => 
      Promise.all(chunks . map(chunk => memcached.write(makeChunkKey(guid, i++), chunk)))
    ) .
    then(() => memcached.write(key, guid + ':' + i));
}

function get(key) {
  return memcached.read(key) .
    then(blob_info => blob_info.split(':')) .
    then(([guid, chunk_num]) => 
      Promise.all(
        new Array(chunk_num) . fill() . map((e, i) => 
          memcached.read(makeChunkKey(guid, i)))
      )) . 
    then(assemble);
}