/**
* paxos_retrieve - Ask the originator of request data to send us data which
* we do not have in our cache.
*
* We call this function when and only when we are issued a commit for an
* instance whose associated request is not in our request cache.
*/
int
paxos_retrieve(struct paxos_instance *inst)
{
int r;
struct paxos_header hdr;
struct paxos_acceptor *acc;
struct paxos_yak py;
// Initialize a header. We set ph_inum to the instance number of the
// request.
header_init(&hdr, OP_RETRIEVE, inst->pi_hdr.ph_inum);
// Pack the retrieve.
paxos_payload_init(&py, 2);
paxos_header_pack(&py, &hdr);
paxos_payload_begin_array(&py, 2);
paxos_paxid_pack(&py, pax->self_id);
paxos_value_pack(&py, &inst->pi_val);
// Determine the request originator and send. If we are no longer connected
// to the request originator, broadcast the retrieve instead.
acc = acceptor_find(&pax->alist, inst->pi_val.pv_reqid.id);
if (acc == NULL || acc->pa_peer == NULL) {
r = paxos_broadcast(&py);
} else {
r = paxos_send(acc, &py);
}
paxos_payload_destroy(&py);
return r;
}
/**
* acceptor_last - Send the instance number of our last contiguous learn to
* the proposer.
*/
int acceptor_last(struct paxos_header *hdr)
{
int r;
struct yakyak yy;
// Modify the header opcode.
hdr->ph_opcode = OP_LAST;
// Pack and send the response.
yakyak_init(&yy, 2);
paxos_header_pack(&yy, hdr);
paxos_paxid_pack(&yy, pax->ihole - 1);
r = paxos_send_to_proposer(&yy);
yakyak_destroy(&yy);
return r;
}
/**
* proposer_truncate - Command all acceptors to drop the contiguous prefix
* of Paxos instances for which every participant has learned.
*/
int
proposer_truncate(struct paxos_header *hdr)
{
int r;
struct yakyak yy;
// Obtain our own last contiguous learn.
if (pax->ihole - 1 < pax->sync->ps_last) {
pax->sync->ps_last = pax->ihole - 1;
}
// Record the sync point.
pax->sync_prev = pax->sync->ps_last;
// Make this instance our new ibase; this ensures that our list always has
// at least one committed instance.
assert(pax->sync->ps_last >= pax->ibase);
pax->ibase = pax->sync->ps_last;
// Modify the header.
hdr->ph_opcode = OP_TRUNCATE;
// Pack a truncate.
yakyak_init(&yy, 2);
paxos_header_pack(&yy, hdr);
paxos_paxid_pack(&yy, pax->ibase);
// Broadcast it.
r = paxos_broadcast(&yy);
yakyak_destroy(&yy);
if (r) {
return r;
}
// Do the truncate (< pax->ibase).
ilist_truncate_prefix(&pax->ilist, pax->ibase);
// End the sync.
g_free(pax->sync);
pax->sync = NULL;
return 0;
}