From fc9c952ba86f6fc9ae55cecb153809180ff517c3 Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Mon, 8 Jun 2020 18:19:55 -0700
Subject: [PATCH] ircd::db: Add parallel read suite to internal interface.

---
 ircd/db.cc | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 ircd/db.h  |  3 ++
 2 files changed, 94 insertions(+)

diff --git a/ircd/db.cc b/ircd/db.cc
index 427730917..1b1913796 100644
--- a/ircd/db.cc
+++ b/ircd/db.cc
@@ -7964,6 +7964,97 @@ ircd::db::_seek(database::column &c,
 	return ret;
 }
 
+//
+// parallel read suite
+//
+
+namespace ircd::db
+{
+	static void _seek(const vector_view<_read_op> &, const vector_view<rocksdb::Status> &, const vector_view<rocksdb::PinnableSlice> &, const rocksdb::ReadOptions &);
+}
+
+bool
+ircd::db::_read(const vector_view<_read_op> &op,
+                const rocksdb::ReadOptions &ropts,
+                const _read_closure &closure)
+{
+	assert(op.size() >= 1);
+	assert(op.size() <= IOV_MAX);
+	const size_t &num
+	{
+		op.size()
+	};
+
+	rocksdb::Status status[num];
+	rocksdb::PinnableSlice val[num];
+	_seek(op, {status, num}, {val, num}, ropts);
+	if(closure) for(size_t i(0); i < op.size(); ++i)
+	{
+		const column::delta &delta
+		{
+			std::get<1>(op[i]), slice(val[i])
+		};
+
+		if(!closure(std::get<0>(op[i]), delta, status[i]))
+			return false;
+	}
+
+	return true;
+}
+
+void
+ircd::db::_seek(const vector_view<_read_op> &op,
+                const vector_view<rocksdb::Status> &ret,
+                const vector_view<rocksdb::PinnableSlice> &val,
+                const rocksdb::ReadOptions &ropts)
+{
+	assert(ret.size() == op.size());
+	assert(ret.size() == val.size());
+
+	const ctx::stack_usage_assertion sua;
+	const ctx::uninterruptible::nothrow ui;
+
+	assert(op.size() >= 1);
+	database &d(std::get<0>(op[0]));
+	const size_t &num
+	{
+		op.size()
+	};
+
+	rocksdb::Slice key[num];
+	std::transform(begin(op), end(op), key, []
+	(const auto &op)
+	{
+		return slice(std::get<1>(op));
+	});
+
+	rocksdb::ColumnFamilyHandle *cf[num];
+	std::transform(begin(op), end(op), cf, []
+	(auto &op_)
+	{
+		auto &op(const_cast<_read_op &>(op_));
+		database::column &c(std::get<column>(op));
+		return static_cast<rocksdb::ColumnFamilyHandle *>(c);
+	});
+
+	#ifdef RB_DEBUG_DB_SEEK
+	const ircd::timer timer;
+	#endif
+
+	d.d->MultiGet(ropts, num, cf, key, val.data(), ret.data());
+
+	#ifdef RB_DEBUG_DB_SEEK
+	log::debug
+	{
+		log, "[%s] %lu:%lu SEEK parallel:%zu in %ld$us",
+		name(d),
+		sequence(d),
+		sequence(opts.snapshot),
+		ret.size(),
+		timer.at<microseconds>().count(),
+	};
+	#endif
+}
 
 //
 // iterator seek suite
diff --git a/ircd/db.h b/ircd/db.h
index 9ba8ef207..96070757a 100644
--- a/ircd/db.h
+++ b/ircd/db.h
@@ -121,6 +121,9 @@ namespace ircd::db
 	std::pair<string_view, string_view> operator*(const rocksdb::Iterator &);
 
 	// [GET] read suite
+	using _read_op = std::tuple<column, string_view>;
+	using _read_closure = std::function<bool (column &, const column::delta &, const rocksdb::Status &)>;
+	bool _read(const vector_view<_read_op> &, const rocksdb::ReadOptions &, const _read_closure & = {});
 	size_t _read(std::nothrow_t, column &, const string_view &key, const rocksdb::ReadOptions &, const column::view_closure & = {});
 	size_t _read(column &, const string_view &key, const rocksdb::ReadOptions &, const column::view_closure & = {});