ircd:Ⓜ️:vm: Add array-wide reference event_id pre-prefetcher.

include/ircd/m/vm/eval.h

@@ -22,6 +22,7 @@ namespace ircd::m::vm
 	string_view loghead(const mutable_buffer &, const eval &);
 	string_view loghead(const eval &);    // single tls buffer
 
+	size_t prefetch_refs(const eval &);
 	size_t fetch_keys(const eval &);
 }
 

include/ircd/m/vm/opts.h

@@ -105,6 +105,12 @@ struct ircd::m::vm::opts
 	/// perform a parallel/mass fetch before proceeding with the evals.
 	bool mfetch_keys {true};
 
+	/// Whether to launch prefetches for all event_id's (found at standard
+	/// locations) from the input vector, in addition to some other related
+	/// local db prefetches. Disabled by default because it operates prior
+	/// to verification and access phases; can be enabled explicitly.
+	bool mprefetch_refs {false};
+
 	/// Throws fault::EVENT if *all* of the prev_events do not exist locally.
 	/// This is used to enforce that at least one path is traversable. This
 	/// test is conducted after waiting if fetch_prev and fetch_prev_wait.

matrix/vm_eval.cc

@@ -78,6 +78,27 @@ ircd::m::vm::fetch_keys(const eval &eval)
 	return fetched;
 }
 
+size_t
+ircd::m::vm::prefetch_refs(const eval &eval)
+{
+	assert(eval.opts);
+	const dbs::write_opts &wopts
+	{
+		eval.opts->wopts
+	};
+
+	size_t prefetched(0);
+	for(const auto &event : eval.pdus)
+	{
+		if(event.event_id)
+			prefetched += m::prefetch(event.event_id, "_event_idx");
+
+		prefetched += dbs::prefetch(event, wopts);
+	}
+
+	return prefetched;
+}
+
 ircd::string_view
 ircd::m::vm::loghead(const eval &eval)
 {

matrix/vm_execute.cc

@@ -220,8 +220,20 @@ ircd::m::vm::execute(eval &eval,
 	const size_t prefetched_keys
 	{
 		prefetch_keys?
-			fetch_keys(eval):
-			0UL
+			fetch_keys(eval): 0UL
+	};
+
+	const bool prefetch_refs
+	{
+		opts.phase[phase::PREINDEX]
+		&& opts.mprefetch_refs
+		&& events.size() > 1
+	};
+
+	const size_t prefetched_refs
+	{
+		prefetch_refs?
+			vm::prefetch_refs(eval): 0UL
 	};
 
 	size_t accepted(0), existed(0), i, j, k;
@@ -936,7 +948,7 @@ ircd::m::vm::execute_pdu(eval &eval,
 	};
 
 	// Allocate transaction; prefetch dependencies.
-	if(likely(opts.phase[phase::PREINDEX]))
+	if(likely(opts.phase[phase::PREINDEX]) && !opts.mprefetch_refs)
 	{
 		const scope_restore eval_phase
 		{