Function dbSwapDatabases

src/db.cpp:1721–1754

Swap two databases at runtime so that all clients will magically see * the new database even if already connected. Note that the client * structure c->db points to a given DB, so we need to be smarter and * swap the underlying referenced structures, otherwise we would need * to fix all the references to the Redis DB structure. * * Returns C_ERR if at least one of the DB ids are out of range,

 * Returns C_ERR if at least one of the DB ids are out of range, otherwise
 * C_OK is returned. */
int dbSwapDatabases(int id1, int id2) {
    if (id1 < 0 || id1 >= cserver.dbnum ||
        id2 < 0 || id2 >= cserver.dbnum) return C_ERR;
    if (id1 == id2) return C_OK;
    std::swap(g_pserver->db[id1], g_pserver->db[id2]);
    
    //swap db's id too, otherwise db does not match its id
    std::swap(g_pserver->db[id1]->id, g_pserver->db[id2]->id);

    /* Note that we don't swap blocking_keys,
     * ready_keys and watched_keys, since we want clients to
     * remain in the same DB they were. so put them back */
    std::swap(g_pserver->db[id1]->blocking_keys, g_pserver->db[id2]->blocking_keys);
    std::swap(g_pserver->db[id2]->ready_keys, g_pserver->db[id2]->ready_keys);
    std::swap(g_pserver->db[id2]->watched_keys, g_pserver->db[id2]->watched_keys);

    /* Now we need to handle clients blocked on lists: as an effect
     * of swapping the two DBs, a client that was waiting for list
     * X in a given DB, may now actually be unblocked if X happens
     * to exist in the new version of the DB, after the swap.
     *
     * However normally we only do this check for efficiency reasons
     * in dbAdd() when a list is created. So here we need to rescan
     * the list of clients blocked on lists and signal lists as ready
     * if needed.
     *
     * Also the swapdb should make transaction fail if there is any
     * client watching keys */
    scanDatabaseForReadyLists(g_pserver->db[id1]);
    touchAllWatchedKeysInDb(g_pserver->db[id1], g_pserver->db[id2]);
    scanDatabaseForReadyLists(g_pserver->db[id2]);
    touchAllWatchedKeysInDb(g_pserver->db[id2], g_pserver->db[id1]);
    return C_OK;
}

/* SWAPDB db1 db2 */
void swapdbCommand(client *c) {