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rpc helper: write comments + small refactoring of tracing

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This commit is contained in:
Alex Auvolat 2023-11-28 11:12:39 +01:00
parent c539077d30
commit 539af6eac4
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GPG Key ID: 0E496D15096376BE
1 changed files with 88 additions and 17 deletions
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105
src/rpc/rpc_helper.rs
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@ -129,6 +129,12 @@ impl RpcHelper {
N: IntoReq<M> + Send,
H: StreamingEndpointHandler<M>,
{
let tracer = opentelemetry::global::tracer("garage");
let span_name = format!("RPC [{}] to {:?}", endpoint.path(), to);
let mut span = tracer.start(span_name);
span.set_attribute(KeyValue::new("from", format!("{:?}", self.0.our_node_id)));
span.set_attribute(KeyValue::new("to", format!("{:?}", to)));
let metric_tags = [
KeyValue::new("rpc_endpoint", endpoint.path().to_string()),
KeyValue::new("from", format!("{:?}", self.0.our_node_id)),
@ -140,6 +146,7 @@ impl RpcHelper {
let node_id = to.into();
let rpc_call = endpoint
.call_streaming(&node_id, msg, strat.rs_priority)
.with_context(Context::current_with_span(span))
.record_duration(&self.0.metrics.rpc_duration, &metric_tags);
let timeout = async {
@ -182,12 +189,17 @@ impl RpcHelper {
N: IntoReq<M>,
H: StreamingEndpointHandler<M>,
{
let tracer = opentelemetry::global::tracer("garage");
let span_name = format!("RPC [{}] call_many {} nodes", endpoint.path(), to.len());
let span = tracer.start(span_name);
let msg = msg.into_req().map_err(netapp::error::Error::from)?;
let resps = join_all(
to.iter()
.map(|to| self.call(endpoint, *to, msg.clone(), strat)),
)
.with_context(Context::current_with_span(span))
.await;
Ok(to
.iter()
@ -219,6 +231,22 @@ impl RpcHelper {
/// Make a RPC call to multiple servers, returning either a Vec of responses,
/// or an error if quorum could not be reached due to too many errors
///
/// If RequestStrategy has send_all_at_once set, then all requests will be
/// sent at once, and `try_call_many` will return as soon as a quorum of
/// responses is achieved, dropping and cancelling the remaining requests.
///
/// Otherwise, `quorum` requests will be sent at the same time, and if an
/// error response is received, a new request will be sent to replace it.
/// The ordering of nodes to which requests are sent is determined by
/// the `RpcHelper::request_order` function, which takes into account
/// parameters such as node zones and measured ping values.
///
/// In both cases, the basic contract of this function is that even in the
/// absence of failures, the RPC call might not be driven to completion
/// on all of the specified nodes. It is therefore unfit for broadcast
/// write operations where we expect all nodes to successfully store
/// the written date.
pub async fn try_call_many<M, N, H, S>(
&self,
endpoint: &Arc<Endpoint<M, H>>,
@ -235,7 +263,12 @@ impl RpcHelper {
let quorum = strategy.rs_quorum.unwrap_or(to.len());
let tracer = opentelemetry::global::tracer("garage");
let span_name = format!("Read RPC {} to {} of {}", endpoint.path(), quorum, to.len());
let span_name = format!(
"RPC [{}] try_call_many (quorum {}/{})",
endpoint.path(),
quorum,
to.len()
);
let mut span = tracer.start(span_name);
span.set_attribute(KeyValue::new("from", format!("{:?}", self.0.our_node_id)));
@ -266,6 +299,10 @@ impl RpcHelper {
// to reach a quorum, priorizing nodes with the lowest latency.
// When there are errors, we start new requests to compensate.
// TODO: this could be made more aggressive, e.g. if after 2x the
// average ping of a given request, the response is not yet received,
// preemptively send an additional request to any remaining nodes.
// Reorder requests to priorize closeness / low latency
let request_order = self.request_order(to.iter().copied());
let send_all_at_once = strategy.rs_send_all_at_once.unwrap_or(false);
@ -278,9 +315,7 @@ impl RpcHelper {
let self2 = self.clone();
let msg = msg.clone();
let endpoint2 = endpoint.clone();
(to, async move {
self2.call(&endpoint2, to, msg, strategy).await
})
async move { self2.call(&endpoint2, to, msg, strategy).await }
});
// Vectors in which success results and errors will be collected
@ -296,10 +331,8 @@ impl RpcHelper {
// If the current set of requests that are running is not enough to possibly
// reach quorum, start some new requests.
while send_all_at_once || successes.len() + resp_stream.len() < quorum {
if let Some((req_to, fut)) = requests.next() {
let tracer = opentelemetry::global::tracer("garage");
let span = tracer.start(format!("RPC to {:?}", req_to));
resp_stream.push(fut.with_context(Context::current_with_span(span)));
if let Some(fut) = requests.next() {
resp_stream.push(fut)
} else {
break;
}
@ -379,6 +412,25 @@ impl RpcHelper {
.collect::<Vec<_>>()
}
/// Make a RPC call to multiple servers, returning either a Vec of responses,
/// or an error if quorum could not be reached due to too many errors
///
/// Contrary to try_call_many, this fuction is especially made for broadcast
/// write operations. In particular:
///
/// - The request are sent to all specified nodes as soon as `try_write_many_sets`
/// is invoked.
///
/// - When `try_write_many_sets` returns, all remaining requests that haven't
/// completed move to a background task so that they have a chance to
/// complete successfully if there are no failures.
///
/// In addition, the nodes to which requests should be sent are divided in
/// "quorum sets", and `try_write_many_sets` only returns once a quorum
/// has been validated in each set. This is used in the case of cluster layout
/// changes, where data has to be written both in the old layout and in the
/// new one as long as all nodes have not successfully tranisitionned and
/// moved all data to the new layout.
pub async fn try_write_many_sets<M, N, H, S>(
&self,
endpoint: &Arc<Endpoint<M, H>>,
@ -394,11 +446,11 @@ impl RpcHelper {
{
let quorum = strategy
.rs_quorum
.expect("internal error: missing quroum in try_write_many_sets");
.expect("internal error: missing quorum value in try_write_many_sets");
let tracer = opentelemetry::global::tracer("garage");
let span_name = format!(
"Write RPC {} (quorum {} in {} sets)",
"RPC [{}] try_write_many_sets (quorum {} in {} sets)",
endpoint.path(),
quorum,
to_sets.len()
@ -430,6 +482,8 @@ impl RpcHelper {
{
let msg = msg.into_req().map_err(netapp::error::Error::from)?;
// Peers may appear in many quorum sets. Here, build a list of peers,
// mapping to the index of the quorum sets in which they appear.
let mut peers = HashMap::<Uuid, Vec<usize>>::new();
for (i, set) in to_sets.iter().enumerate() {
for peer in set.iter() {
@ -437,24 +491,30 @@ impl RpcHelper {
}
}
// Send one request to each peer of the quorum sets
let requests = peers.iter().map(|(peer, _)| {
let self2 = self.clone();
let msg = msg.clone();
let endpoint2 = endpoint.clone();
let to = *peer;
let tracer = opentelemetry::global::tracer("garage");
let span = tracer.start(format!("RPC to {:?}", to));
let fut = async move { (to, self2.call(&endpoint2, to, msg, strategy).await) };
fut.with_context(Context::current_with_span(span))
async move { (to, self2.call(&endpoint2, to, msg, strategy).await) }
});
let mut resp_stream = requests.collect::<FuturesUnordered<_>>();
// Success and error responses will be collected in these two vectors
let mut successes = vec![];
let mut errors = vec![];
// `set_counters` is used to keep track of how many success and error
// responses are received within each quorum set. When a node returns
// its response, it counts as a sucess/an error for all of the quorum
// sets which it is part of.
let mut set_counters = vec![(0, 0); to_sets.len()];
// Drive requests to completion
while let Some((node, resp)) = resp_stream.next().await {
// Store the response in the correct vector and increment the
// appropriate counters
match resp {
Ok(msg) => {
for set in peers.get(&node).unwrap().iter() {
@ -470,9 +530,8 @@ impl RpcHelper {
}
}
// If we have a quorum of ok in all quorum sets, then it's a success!
if set_counters.iter().all(|(ok_cnt, _)| *ok_cnt >= quorum) {
// Success
// Continue all other requets in background
tokio::spawn(async move {
resp_stream.collect::<Vec<(Uuid, Result<_, _>)>>().await;
@ -481,16 +540,28 @@ impl RpcHelper {
return Ok(successes);
}
// If there is a quorum set for which too many errors were received,
// we know it's impossible to get a quorum, so return immediately.
if set_counters
.iter()
.enumerate()
.any(|(i, (_, err_cnt))| err_cnt + quorum > to_sets[i].len())
{
// Too many errors in this set, we know we won't get a quorum
break;
}
}
// At this point, there is no quorum and we know that a quorum
// will never be achieved. Currently, we drop all remaining requests.
// Should we still move them to background so that they can continue
// for non-failed nodes? Not doing so has no impact on correctness,
// but it means that more cancellation messages will be sent. Idk.
// (When an in-progress request future is dropped, Netapp automatically
// sends a cancellation message to the remote node to inform it that
// the result is no longer needed. In turn, if the remote node receives
// the cancellation message in time, it interrupts the task of the
// running request handler.)
// Failure, could not get quorum
let errors = errors.iter().map(|e| format!("{}", e)).collect::<Vec<_>>();
Err(Error::Quorum(