Key-Value store

[dworkin]

Cloudlib now has support for persistent key-value stores. A key-value store is like a mapping which can grow to be arbitrarily large. The mapping index must always be a string, and the corresponding value must not be a persistent object; otherwise, anything goes.

# include <KVstore.h>

    store = new KVstore(nodeSize);   /* create new K/V store */
    store["index"] = someValue;      /* assign value */
    value = store["index"];          /* retrieve value */
    store["index"] = nil;            /* remove index/value from store */
    store->remove();                 /* remove entire store, including the persistent objects that contain it */

Key-value stores are implemented as B+ trees, with each node a persistent object. nodeSize is how many keys can be stored in one persistent object. A suitable value would depend on the sector size configured for DGD; it would be best not to let internal nodes in the B+ tree use more than one sector.

Key-value stores permit concurrent modifications in Hydra.

Key-value stores are also iterable.

[dworkin]

The KVstore works only with LPC string indices. The code below extends it to use String indices.

# include <KVstore.h>
# include <String.h>

inherit KVstore;


mixed get(String key)
{
    if (!key) {
	error("Invalid key");
    }
    return ::get(key->utf8());
}

void set(String key, mixed value)
{
    if (!key) {
	error("Invalid key");
    }
    ::set(key->utf8(), value);
}

static void operator[]= (String index, mixed value)
{
    set(index, value);
}

static mixed operator[] (String index)
{
    return get(index);
}

mixed iteratorStart(mixed from, mixed to)
{
    String first, last;

    first = from;
    last = to;
    return ::iteratorStart((first) ? first->utf8() : nil,
			   (last) ? last->utf8() : nil);
}

mixed *iteratorNext(mixed state)
{
    mixed *keyVal;

    ({ state, keyVal }) = ::iteratorNext(state);
    if (keyVal[0]) {
	keyVal[0] = new String(keyVal[0], "UTF8");
    }
    return ({ state, keyVal });
}