stale data in cache with binary protocol

The textual protocol does not allow stale data to persist in the cache in
case of memory allocation errors. The binary protocol allows it.

e.g:

Textual protocol:
////////////////////////
static void process_update_command(conn *c, token_t *tokens, const size_t
ntokens, int comm, bool handle_cas) {
.
.
.
    it = item_alloc(key, nkey, flags, realtime(exptime), vlen+2);

    if (it == 0) {
        if (! item_size_ok(nkey, flags, vlen + 2))
            out_string(c, "SERVER_ERROR object too large for cache");
        else
            out_string(c, "SERVER_ERROR out of memory storing object");
        /* swallow the data line */
        c->write_and_go = conn_swallow;
        c->sbytes = vlen + 2;

        /* Avoid stale data persisting in cache because we failed alloc.
         * Unacceptable for SET. Anywhere else too? */
        if (comm == NREAD_SET) {
            it = item_get(key, nkey);
            if (it) {
                item_unlink(it);
                item_remove(it);
            }
        }
        return;
    }
.
.
.
}

Textual protocol:
////////////////////////

int do_store_item(item *it, int comm, conn *c) {
.
.
.
        if (comm == NREAD_APPEND || comm == NREAD_PREPEND) {
.
.
                new_it = do_item_alloc(key, it->nkey, flags,
old_it->exptime, it->nbytes + old_it->nbytes - 2 /* CRLF */);

                if (new_it == NULL) {
                    /* SERVER_ERROR out of memory */
                    if (old_it != NULL)
                        do_item_remove(old_it);
                    return 0;
                }
.
.
.
}

Binary protocol:
////////////////////////
static void process_bin_update(conn *c) {
.
.
.
    it = item_alloc(key, nkey, req->message.body.flags,
            realtime(req->message.body.expiration), vlen+2);

    if (it == 0) {
        if (! item_size_ok(nkey, req->message.body.flags, vlen + 2)) {
            write_bin_error(c, PROTOCOL_BINARY_RESPONSE_E2BIG, vlen);
        } else {
            write_bin_error(c, PROTOCOL_BINARY_RESPONSE_ENOMEM, vlen);
        }
        /* swallow the data line */
        c->write_and_go = conn_swallow;
        return;
    }
.
.
.
}

Binary protocol:
////////////////////////
static void process_bin_append_prepend(conn *c) {
.
.
.
    it = item_alloc(key, nkey, 0, 0, vlen+2);

    if (it == 0) {
        if (! item_size_ok(nkey, 0, vlen + 2)) {
            write_bin_error(c, PROTOCOL_BINARY_RESPONSE_E2BIG, vlen);
        } else {
            write_bin_error(c, PROTOCOL_BINARY_RESPONSE_ENOMEM, vlen);
        }
        /* swallow the data line */
        c->write_and_go = conn_swallow;
        return;
    }
.
.
.
}
Original issue reported on code.google.com by Victor.K...@gmail.com on 17 Dec 2008 at 6:48
Jdesk / memcached

stale data in cache with binary protocol #8
