Function replicationCacheMasterUsingMyself

app/redis-6.2.6/src/replication.c:2949–2972

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(void) {
    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.");

    /* This will be used to populate the field server.master->reploff
     * by replicationCreateMasterClient(). We'll later set the created
     * master as server.cached_master, so the replica will use such
     * offset for PSYNC. */
    server.master_initial_offset = server.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(NULL,-1);

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

    /* Set as cached master. */
    unlinkClient(server.master);
    server.cached_master = server.master;
    server.master = NULL;
}

/* Free a cached master, called when there are no longer the conditions for
 * a partial resync on reconnection. */