Skip to content

Commit

Permalink
hostdb: remove latency with cache misses (#11764)
Browse files Browse the repository at this point in the history 
Co-authored-by: Chris McFarlen <[email protected]>
  • Loading branch information
@cmcfarlen
cmcfarlen and Chris McFarlen authored Sep 16, 2024
1 parent 714aa15 commit 2456d4c
Show file tree
Hide file tree
Showing 2 changed files with 79 additions and 67 deletions.
111 changes: 61 additions & 50 deletions src/iocore/hostdb/HostDB.cc
View file
Original file line number Diff line number Diff line change
Expand Up @@ -489,6 +489,38 @@ db_mark_for(IpAddr const &ip)
return ip.isIp6() ? HOSTDB_MARK_IPV6 : HOSTDB_MARK_IPV4;
}

HostDBRecord::Handle
probe_ip(HostDBHash const &hash)
{
HostDBRecord::Handle result;

if (hash.is_byname()) {
Dbg(dbg_ctl_hostdb, "DNS %.*s", int(hash.host_name.size()), hash.host_name.data());
IpAddr tip;
if (0 == tip.load(hash.host_name)) {
result = HostDBRecord::Handle{HostDBRecord::alloc(hash.host_name, 1)};
result->af_family = tip.family();
auto &info = result->rr_info()[0];
info.assign(tip);
}
}

return result;
}

HostDBRecord::Handle
probe_hostfile(HostDBHash const &hash)
{
HostDBRecord::Handle result;
// Check if this can be fulfilled by the host file
//
if (auto static_hosts = hostDB.acquire_host_file(); static_hosts) {
result = static_hosts->lookup(hash);
}

return result;
}

HostDBRecord::Handle
probe(HostDBHash const &hash, bool ignore_timeout)
{
Expand All @@ -511,6 +543,10 @@ probe(HostDBHash const &hash, bool ignore_timeout)
record = hostDB.refcountcache->get(folded_hash);
// If there was nothing in the cache-- this is a miss
if (record.get() == nullptr) {
record = probe_ip(hash);
if (!record) {
record = probe_hostfile(hash);
}
return record;
}

Expand Down Expand Up @@ -555,9 +591,10 @@ probe(HostDBHash const &hash, bool ignore_timeout)
Action *
HostDBProcessor::getby(Continuation *cont, cb_process_result_pfn cb_process_result, HostDBHash &hash, Options const &opt)
{
bool force_dns = false;
EThread *thread = this_ethread();
Ptr<ProxyMutex> mutex = thread->mutex;
bool force_dns = false;
bool delay_reschedule = false;
EThread *thread = this_ethread();
Ptr<ProxyMutex> mutex = thread->mutex;
ip_text_buffer ipb;

if (opt.flags & HOSTDB_FORCE_DNS_ALWAYS) {
Expand All @@ -579,6 +616,7 @@ HostDBProcessor::getby(Continuation *cont, cb_process_result_pfn cb_process_resu
} else {
MUTEX_TRY_LOCK(lock, cont->mutex, thread);
if (!lock.is_locked()) {
delay_reschedule = true;
goto Lretry;
}
cont->handleEvent(EVENT_HOST_DB_LOOKUP, nullptr);
Expand Down Expand Up @@ -650,7 +688,11 @@ HostDBProcessor::getby(Continuation *cont, cb_process_result_pfn cb_process_resu
c->init(hash, copt);
SET_CONTINUATION_HANDLER(c, &HostDBContinuation::probeEvent);

c->timeout = thread->schedule_in(c, MUTEX_RETRY_DELAY);
if (delay_reschedule) {
c->timeout = thread->schedule_in(c, MUTEX_RETRY_DELAY);
} else {
thread->schedule_imm(c);
}

return &c->action;
}
Expand Down Expand Up @@ -784,9 +826,9 @@ HostDBContinuation::lookup_done(TextView query_name, ts_seconds answer_ttl, SRVH
{
ink_assert(record);
if (query_name.empty()) {
if (is_byname()) {
if (hash.is_byname()) {
Dbg(dbg_ctl_hostdb, "lookup_done() failed for '%.*s'", int(hash.host_name.size()), hash.host_name.data());
} else if (is_srv()) {
} else if (hash.is_srv()) {
Dbg(dbg_ctl_dns_srv, "SRV failed for '%.*s'", int(hash.host_name.size()), hash.host_name.data());
} else {
ip_text_buffer b;
Expand All @@ -795,9 +837,9 @@ HostDBContinuation::lookup_done(TextView query_name, ts_seconds answer_ttl, SRVH
record->ip_timestamp = hostdb_current_timestamp;
record->ip_timeout_interval = ts_seconds(std::clamp(hostdb_ip_fail_timeout_interval, 1u, HOST_DB_MAX_TTL));

if (is_srv()) {
if (hash.is_srv()) {
record->record_type = HostDBType::SRV;
} else if (!is_byname()) {
} else if (!hash.is_byname()) {
record->record_type = HostDBType::HOST;
}

Expand Down Expand Up @@ -829,9 +871,9 @@ HostDBContinuation::lookup_done(TextView query_name, ts_seconds answer_ttl, SRVH
record->ip_timestamp = hostdb_current_timestamp;
record->ip_timeout_interval = std::clamp(answer_ttl, ts_seconds(1), ts_seconds(HOST_DB_MAX_TTL));

if (is_byname()) {
if (hash.is_byname()) {
Dbg_bw(dbg_ctl_hostdb, "done {} TTL {}", hash.host_name, answer_ttl);
} else if (is_srv()) {
} else if (hash.is_srv()) {
ink_assert(srv && srv->hosts.size() && srv->hosts.size() <= hostdb_round_robin_max_count);

record->record_type = HostDBType::SRV;
Expand Down Expand Up @@ -935,7 +977,7 @@ HostDBContinuation::dnsEvent(int event, HostEnt *e)

// Find the first record and total number of records.
if (!failed) {
if (is_srv()) {
if (hash.is_srv()) {
valid_records = e->srv_hosts.hosts.size();
} else {
void *ptr; // tmp for current entry.
Expand Down Expand Up @@ -978,9 +1020,9 @@ HostDBContinuation::dnsEvent(int event, HostEnt *e)
if (failed && old_r && old_r->serve_stale_but_revalidate()) {
r = old_r;
serve_stale = true;
} else if (is_byname()) {
} else if (hash.is_byname()) {
lookup_done(hash.host_name, ttl, failed ? nullptr : &e->srv_hosts, r);
} else if (is_srv()) {
} else if (hash.is_srv()) {
lookup_done(hash.host_name, /* hostname */
ttl, /* ttl in seconds */
failed ? nullptr : &e->srv_hosts, r);
Expand All @@ -993,7 +1035,7 @@ HostDBContinuation::dnsEvent(int event, HostEnt *e)
if (!failed) { // implies r != old_r
auto rr_info = r->rr_info();
// Fill in record type specific data.
if (is_srv()) {
if (hash.is_srv()) {
char *pos = rr_info.rebind<char>().end();
SRV *q[valid_records];
ink_assert(valid_records <= (int)hostdb_round_robin_max_count);
Expand Down Expand Up @@ -1067,7 +1109,7 @@ HostDBContinuation::dnsEvent(int event, HostEnt *e)
if (action.continuation->mutex) {
ink_release_assert(action.continuation->mutex == action.mutex);
}
reply_to_cont(action.continuation, r.get(), is_srv());
reply_to_cont(action.continuation, r.get(), hash.is_srv());
}
need_to_reschedule = false;
}
Expand Down Expand Up @@ -1190,14 +1232,14 @@ HostDBContinuation::probeEvent(int /* event ATS_UNUSED */, Event *e)
if (!force_dns) {
// Do the probe
//
Ptr<HostDBRecord> r = probe(hash, false);
HostDBRecord::Handle r = probe(hash, false);

if (r) {
Metrics::Counter::increment(hostdb_rsb.total_hits);
}

if (action.continuation && r) {
reply_to_cont(action.continuation, r.get(), is_srv());
reply_to_cont(action.continuation, r.get(), hash.is_srv());
}

// If it succeeds or it was a remote probe, we are done
Expand Down Expand Up @@ -1283,37 +1325,6 @@ void
HostDBContinuation::do_dns()
{
ink_assert(!action.cancelled);
if (is_byname()) {
Dbg(dbg_ctl_hostdb, "DNS %.*s", int(hash.host_name.size()), hash.host_name.data());
IpAddr tip;
if (0 == tip.load(hash.host_name)) {
// Need to consider if this is necessary - could the record in ResolveInfo be left null and
// just the resolved address set?
if (action.continuation) {
HostDBRecord::Handle r{HostDBRecord::alloc(hash.host_name, 1)};
r->af_family = tip.family();
auto &info = r->rr_info()[0];
info.assign(tip);
// tricksy - @a reply_to_cont must use an intrusive pointer to @a r if it needs to persist
// @a r doesn't go out of scope until after this returns. This continuation shares the mutex
// of the target continuation therefore this is always dispatched synchronously.
reply_to_cont(action.continuation, r.get());
}
hostdb_cont_free(this);
return;
}
}

// Check if this can be fulfilled by the host file
if (auto static_hosts = hostDB.acquire_host_file(); static_hosts) {
if (auto r = static_hosts->lookup(hash); r && action.continuation) {
// Set the TTL based on how often we stat() the host file
r = lookup_done(r->name_view(), static_hosts->ttl, nullptr, r);
reply_to_cont(action.continuation, r.get());
hostdb_cont_free(this);
return;
}
}

if (hostdb_lookup_timeout) {
EThread *thread = this_ethread();
Expand All @@ -1326,12 +1337,12 @@ HostDBContinuation::do_dns()
opt.timeout = dns_lookup_timeout;
opt.host_res_style = host_res_style_for(hash.db_mark);
SET_HANDLER(&HostDBContinuation::dnsEvent);
if (is_byname()) {
if (hash.is_byname()) {
if (hash.dns_server) {
opt.handler = hash.dns_server->x_dnsH;
}
pending_action = dnsProcessor.gethostbyname(this, hash.host_name, opt);
} else if (is_srv()) {
} else if (hash.is_srv()) {
Dbg(dbg_ctl_dns_srv, "SRV lookup of %.*s", int(hash.host_name.size()), hash.host_name.data());
pending_action = dnsProcessor.getSRVbyname(this, hash.host_name, opt);
} else {
Expand Down
35 changes: 18 additions & 17 deletions src/iocore/hostdb/P_HostDBProcessor.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -197,6 +197,24 @@ struct HostDBHash {
{
return this->set_host(swoc::TextView{name, strlen(name)});
}

bool
is_byname() const
{
return db_mark == HOSTDB_MARK_IPV4 || db_mark == HOSTDB_MARK_IPV6;
}

bool
is_srv() const
{
return db_mark == HOSTDB_MARK_SRV;
}

bool
is_reverse() const
{
return !is_byname() && !is_srv();
}
};

//
Expand Down Expand Up @@ -239,23 +257,6 @@ struct HostDBContinuation : public Continuation {
/// Recompute the hash and update ancillary values.
void refresh_hash();
void do_dns();
bool
is_byname()
{
return hash.db_mark == HOSTDB_MARK_IPV4 || hash.db_mark == HOSTDB_MARK_IPV6;
}
bool
is_srv()
{
return hash.db_mark == HOSTDB_MARK_SRV;
}

bool
is_reverse()
{
return !is_byname() && !is_srv();
}

Ptr<HostDBRecord>
lookup_done(const char *query_name, ts_seconds answer_ttl, SRVHosts *s = nullptr, Ptr<HostDBRecord> record = Ptr<HostDBRecord>{})
{
Expand Down

0 comments on commit 2456d4c

Please sign in to comment.