Function replicationCacheMasterUsingMyself

src/replication.cpp:4381–4411

This function is called when a master is turend into a slave, in order to * create from scratch a cached master for the new client, that will allow * to PSYNC with the slave that was promoted as the new master after a * failover. * * Assuming this instance was previously the master instance of the new master, * the new master will accept its replication ID, and potentiall also the * current

 * current offset if no data was lost during the failover. So we use our
 * current replication ID and offset in order to synthesize a cached master. */
void replicationCacheMasterUsingMyself(redisMaster *mi) {
    serverLog(LL_NOTICE,
        "Before turning into a replica, using my own master parameters "
        "to synthesize a cached master: I may be able to synchronize with "
        "the new master with just a partial transfer.");

    if (mi->cached_master != nullptr)
    {
        // This can happen on first load of the RDB, the master we created in config load is stale
        freeClient(mi->cached_master);
    }

    /* This will be used to populate the field g_pserver->master->reploff
     * by replicationCreateMasterClient(). We'll later set the created
     * master as g_pserver->cached_master, so the replica will use such
     * offset for PSYNC. */
    mi->master_initial_offset = g_pserver->master_repl_offset;

    /* The master client we create can be set to any DBID, because
     * the new master will start its replication stream with SELECT. */
    replicationCreateMasterClient(mi,NULL,-1);
    std::lock_guard<decltype(mi->master->lock)> lock(mi->master->lock);

    /* Use our own ID / offset. */
    memcpy(mi->master->replid, g_pserver->replid, sizeof(g_pserver->replid));

    /* Set as cached master. */
    unlinkClient(mi->master);
    mi->cached_master = mi->master;
    mi->master = NULL;
}

/* This function is called when reloading master info from an RDB in Active Replica mode.
 * It creates a cached master client using the info contained in the redisMaster struct.