ircd::db: Add preliminary support for secondary-mode if available.

construct/construct.cc

@@ -38,6 +38,7 @@ bool yes6;
 bool norun;
 bool read_only;
 bool write_avoid;
+bool slave;
 std::array<bool, 7> smoketest;
 bool soft_assert;
 bool nomatrix;
@@ -70,6 +71,7 @@ lgetopt opts[]
 	{ "norun",      &norun,         lgetopt::BOOL,    "[debug & testing only] Initialize but never run the event loop" },
 	{ "ro",         &read_only,     lgetopt::BOOL,    "Read-only mode. No writes to database allowed" },
 	{ "wa",         &write_avoid,   lgetopt::BOOL,    "Like read-only mode, but writes permitted if triggered" },
+	{ "slave",      &slave,         lgetopt::BOOL,    "Like read-only mode; allows multiple instances of server" },
 	{ "smoketest",  &smoketest[0],  lgetopt::BOOL,    "Starts and stops the daemon to return success" },
 	{ "sassert",    &soft_assert,   lgetopt::BOOL,    "Softens assertion effects in debug mode" },
 	{ "nomatrix",   &nomatrix,      lgetopt::BOOL,    "Prevent loading the matrix application module" },
@@ -483,6 +485,9 @@ applyargs()
 	if(read_only)
 		ircd::read_only.set("true");
 
+	if(slave)
+		ircd::db::open_slave.set("true");
+
 	// read_only implies write_avoid.
 	if(write_avoid || read_only)
 		ircd::write_avoid.set("true");

include/ircd/db/database.h

@@ -19,6 +19,7 @@ namespace ircd::db
 	extern conf::item<bool> open_check;
 	extern conf::item<std::string> open_recover;
 	extern conf::item<bool> open_repair;
+	extern conf::item<bool> open_slave;
 	extern conf::item<bool> auto_compact;
 
 	// General information
@@ -53,6 +54,7 @@ namespace ircd::db
 	void bgcancel(database &, const bool &blocking = true);
 	void bgcontinue(database &);
 	void bgpause(database &);
+	void refresh(database &);
 	void resume(database &);
 	void check(database &, const string_view &file);
 	void check(database &);
@@ -105,7 +107,7 @@ struct ircd::db::database
 	uint64_t checkpoint;
 	std::string path;
 	std::string optstr;
-	bool fsck, read_only;
+	bool fsck, slave, read_only;
 	std::shared_ptr<struct env> env;
 	std::shared_ptr<struct stats> stats;
 	std::shared_ptr<struct logger> logger;

ircd/db.cc

@@ -453,6 +453,17 @@ ircd::db::auto_compact
 	{ "persist",  false                  },
 };
 
+/// Conf item dictates whether databases will be opened in slave mode; this
+/// is a recent feature of RocksDB which may not be available. It allows two
+/// instances of a database, so long as only one is not opened as a slave.
+decltype(ircd::db::open_slave)
+ircd::db::open_slave
+{
+	{ "name",     "ircd.db.open.slave" },
+	{ "default",  false                },
+	{ "persist",  false                },
+};
+
 void
 ircd::db::sync(database &d)
 {
@@ -647,6 +658,27 @@ ircd::db::resume(database &d)
 	};
 }
 
+void
+ircd::db::refresh(database &d)
+{
+	assert(d.d);
+
+	throw_on_error
+	{
+		#ifdef IRCD_DB_HAS_SECONDARY
+		d.d->TryCatchUpWithPrimary()
+		#else
+		rocksdb::Status::NotSupported(slice("Slave mode not supported by this RocksDB"_sv))
+		#endif
+	};
+
+	log::debug
+	{
+		log, "[%s] Caught up with primary database.",
+		name(d)
+	};
+}
+
 void
 ircd::db::bgpause(database &d)
 {
@@ -1170,6 +1202,10 @@ try
 {
 	db::open_repair
 }
+,slave
+{
+	db::open_slave
+}
 ,read_only
 {
 	ircd::read_only
@@ -1480,7 +1516,16 @@ try
 
 	// Open DB into ptr
 	rocksdb::DB *ptr;
-	if(read_only)
+	if(slave)
+		throw_on_error
+		{
+			#ifdef IRCD_DB_HAS_SECONDARY
+			rocksdb::DB::OpenAsSecondary(*opts, path, "/tmp/slave", columns, &handles, &ptr)
+			#else
+			rocksdb::Status::NotSupported(slice("Slave mode not supported by this RocksDB"_sv))
+			#endif
+		};
+	else if(read_only)
 		throw_on_error
 		{
 			rocksdb::DB::OpenForReadOnly(*opts, path, columns, &handles, &ptr)

ircd/db_has.h

@@ -19,6 +19,12 @@
 	#define IRCD_DB_HAS_ENV_PRIO_USER
 #endif
 
+#if ROCKSDB_MAJOR > 6 \
+|| (ROCKSDB_MAJOR == 6 && ROCKSDB_MINOR > 1) \
+|| (ROCKSDB_MAJOR == 6 && ROCKSDB_MINOR == 1 && ROCKSDB_PATCH >= 1)
+	#define IRCD_DB_HAS_SECONDARY
+#endif
+
 #if ROCKSDB_MAJOR > 6 \
 || (ROCKSDB_MAJOR == 6 && ROCKSDB_MINOR > 2) \
 || (ROCKSDB_MAJOR == 6 && ROCKSDB_MINOR == 2 && ROCKSDB_PATCH >= 2)

modules/console.cc

@@ -2834,6 +2834,35 @@ catch(const std::out_of_range &e)
 	return true;
 }
 
+bool
+console_cmd__db__refresh(opt &out, const string_view &line)
+try
+{
+	const params param{line, " ",
+	{
+		"dbname",
+	}};
+
+	const auto dbname
+	{
+		param.at(0)
+	};
+
+	auto &database
+	{
+		db::database::get(dbname)
+	};
+
+	refresh(database);
+	out << "done" << std::endl;
+	return true;
+}
+catch(const std::out_of_range &e)
+{
+	out << "No open database by that name" << std::endl;
+	return true;
+}
+
 bool
 console_cmd__db__loglevel(opt &out, const string_view &line)
 try