/*
 * Copyright (C) 2018-present ScyllaDB
 */

/*
 * SPDX-License-Identifier: AGPL-3.0-or-later
 */

#include <seastar/core/coroutine.hh>
#include <seastar/coroutine/maybe_yield.hh>
#include <seastar/coroutine/parallel_for_each.hh>
#include <seastar/util/closeable.hh>
#include "distributed_loader.hh"
#include "replica/database.hh"
#include "db/config.hh"
#include "db/system_keyspace.hh"
#include "db/system_distributed_keyspace.hh"
#include "db/schema_tables.hh"
#include "utils/lister.hh"
#include "compaction/compaction.hh"
#include "compaction/compaction_manager.hh"
#include "sstables/sstables.hh"
#include "sstables/sstables_manager.hh"
#include "sstables/sstable_directory.hh"
#include "service/priority_manager.hh"
#include "auth/common.hh"
#include "tracing/trace_keyspace_helper.hh"
#include "db/view/view_update_checks.hh"
#include <unordered_map>
#include <boost/range/adaptor/map.hpp>
#include <boost/range/algorithm/min_element.hpp>
#include "db/view/view_update_generator.hh"
#include "utils/directories.hh"

extern logging::logger dblog;

static const std::unordered_set<std::string_view> system_keyspaces = {
                db::system_keyspace::NAME, db::schema_tables::NAME
};

// Not super nice. Adding statefulness to the file. 
static std::unordered_set<sstring> load_prio_keyspaces;
static bool population_started = false;

void replica::distributed_loader::mark_keyspace_as_load_prio(const sstring& ks) {
    assert(!population_started);
    load_prio_keyspaces.insert(ks);
}

bool is_system_keyspace(std::string_view name) {
    return system_keyspaces.contains(name);
}

bool is_load_prio_keyspace(const sstring& name) {
    return load_prio_keyspaces.contains(name);
}

static const std::unordered_set<std::string_view> internal_keyspaces = {
        db::system_distributed_keyspace::NAME,
        db::system_distributed_keyspace::NAME_EVERYWHERE,
        db::system_keyspace::NAME,
        db::schema_tables::NAME,
        auth::meta::AUTH_KS,
        tracing::trace_keyspace_helper::KEYSPACE_NAME
};

bool is_internal_keyspace(std::string_view name) {
    return internal_keyspaces.contains(name);
}

namespace replica {

static io_error_handler error_handler_for_upload_dir() {
    return [] (std::exception_ptr eptr) {
        // do nothing about sstable exception and caller will just rethrow it.
    };
}

io_error_handler error_handler_gen_for_upload_dir(disk_error_signal_type& dummy) {
    return error_handler_for_upload_dir();
}

// global_column_family_ptr provides a way to easily retrieve local instance of a given column family.
class global_column_family_ptr {
    distributed<replica::database>& _db;
    table_id _id;
private:
    replica::column_family& get() const { return _db.local().find_column_family(_id); }
public:
    global_column_family_ptr(distributed<replica::database>& db, sstring ks_name, sstring cf_name)
        : _db(db)
        , _id(_db.local().find_column_family(ks_name, cf_name).schema()->id()) {
    }

    replica::column_family* operator->() const {
        return &get();
    }
    replica::column_family& operator*() const {
        return get();
    }
};

future<>
distributed_loader::process_sstable_dir(sharded<sstables::sstable_directory>& dir, bool sort_sstables_according_to_owner) {
    co_await dir.invoke_on(0, [] (const sstables::sstable_directory& d) {
        return utils::directories::verify_owner_and_mode(d.sstable_dir());
    });

    co_await dir.invoke_on_all([&dir, sort_sstables_according_to_owner] (sstables::sstable_directory& d) -> future<> {
        // Supposed to be called with the node either down or on behalf of maintenance tasks
        // like nodetool refresh
        co_await d.process_sstable_dir(sort_sstables_according_to_owner);
        co_await d.move_foreign_sstables(dir);
    });

    co_await dir.invoke_on_all(&sstables::sstable_directory::commit_directory_changes);
}

future<>
distributed_loader::lock_table(sharded<sstables::sstable_directory>& dir, sharded<replica::database>& db, sstring ks_name, sstring cf_name) {
    return dir.invoke_on_all([&db, ks_name, cf_name] (sstables::sstable_directory& d) {
        auto& table = db.local().find_column_family(ks_name, cf_name);
        d.store_phaser(table.write_in_progress());
        return make_ready_future<>();
    });
}

// Helper structure for resharding.
//
// Describes the sstables (represented by their foreign_sstable_open_info) that are shared and
// need to be resharded. Each shard will keep one such descriptor, that contains the list of
// SSTables assigned to it, and their total size. The total size is used to make sure we are
// fairly balancing SSTables among shards.
struct reshard_shard_descriptor {
    sstables::sstable_directory::sstable_info_vector info_vec;
    uint64_t uncompressed_data_size = 0;

    bool total_size_smaller(const reshard_shard_descriptor& rhs) const {
        return uncompressed_data_size < rhs.uncompressed_data_size;
    }

    uint64_t size() const {
        return uncompressed_data_size;
    }
};

// Collects shared SSTables from all shards and returns a vector containing them all.
// This function assumes that the list of SSTables can be fairly big so it is careful to
// manipulate it in a do_for_each loop (which yields) instead of using standard accumulators.
future<sstables::sstable_directory::sstable_info_vector>
collect_all_shared_sstables(sharded<sstables::sstable_directory>& dir) {
    auto info_vec = sstables::sstable_directory::sstable_info_vector();

    // We want to make sure that each distributed object reshards about the same amount of data.
    // Each sharded object has its own shared SSTables. We can use a clever algorithm in which they
    // all distributely figure out which SSTables to exchange, but we'll keep it simple and move all
    // their foreign_sstable_open_info to a coordinator (the shard who called this function). We can
    // move in bulk and that's efficient. That shard can then distribute the work among all the
    // others who will reshard.
    auto coordinator = this_shard_id();
    // We will first move all of the foreign open info to temporary storage so that we can sort
    // them. We want to distribute bigger sstables first.
    co_await dir.invoke_on_all([&info_vec, coordinator] (sstables::sstable_directory& d) -> future<> {
        co_await smp::submit_to(coordinator, [&] () -> future<> {
            for (auto& info : d.retrieve_shared_sstables()) {
                info_vec.push_back(std::move(info));
                co_await coroutine::maybe_yield();
            }
        });
    });

    co_return info_vec;
}

// Given a vector of shared sstables to be resharded, distribute it among all shards.
// The vector is first sorted to make sure that we are moving the biggest SSTables first.
//
// Returns a reshard_shard_descriptor per shard indicating the work that each shard has to do.
future<std::vector<reshard_shard_descriptor>>
distribute_reshard_jobs(sstables::sstable_directory::sstable_info_vector source) {
    auto destinations = std::vector<reshard_shard_descriptor>(smp::count);

    std::sort(source.begin(), source.end(), [] (const sstables::foreign_sstable_open_info& a, const sstables::foreign_sstable_open_info& b) {
        // Sort on descending SSTable sizes.
        return a.uncompressed_data_size > b.uncompressed_data_size;
    });

    for (auto& info : source) {
        auto shard_it = boost::min_element(destinations, std::mem_fn(&reshard_shard_descriptor::total_size_smaller));
        shard_it->uncompressed_data_size += info.uncompressed_data_size;
        shard_it->info_vec.push_back(std::move(info));
        co_await coroutine::maybe_yield();
    }

    co_return destinations;
}

future<> run_resharding_jobs(sharded<sstables::sstable_directory>& dir, std::vector<reshard_shard_descriptor> reshard_jobs,
                             sharded<replica::database>& db, sstring ks_name, sstring table_name, sstables::compaction_sstable_creator_fn creator) {

    uint64_t total_size = boost::accumulate(reshard_jobs | boost::adaptors::transformed(std::mem_fn(&reshard_shard_descriptor::size)), uint64_t(0));
    if (total_size == 0) {
        co_return;
    }

    auto start = std::chrono::steady_clock::now();
    dblog.info("{}", fmt::format("Resharding {} for {}.{}", sstables::pretty_printed_data_size(total_size), ks_name, table_name));

    co_await dir.invoke_on_all([&] (sstables::sstable_directory& d) -> future<> {
        auto& table = db.local().find_column_family(ks_name, table_name);
        auto info_vec = std::move(reshard_jobs[this_shard_id()].info_vec);
        auto& cm = db.local().get_compaction_manager();
        auto max_threshold = table.schema()->max_compaction_threshold();
        co_await d.reshard(std::move(info_vec), cm, table, max_threshold, creator);
        co_await d.move_foreign_sstables(dir);
    });

    auto duration = std::chrono::duration_cast<std::chrono::duration<float>>(std::chrono::steady_clock::now() - start);
    dblog.info("{}", fmt::format("Resharded {} for {}.{} in {:.2f} seconds, {}", sstables::pretty_printed_data_size(total_size), ks_name, table_name, duration.count(), sstables::pretty_printed_throughput(total_size, duration)));
}

// Global resharding function. Done in two parts:
//  - The first part spreads the foreign_sstable_open_info across shards so that all of them are
//    resharding about the same amount of data
//  - The second part calls each shard's distributed object to reshard the SSTables they were
//    assigned.
future<>
distributed_loader::reshard(sharded<sstables::sstable_directory>& dir, sharded<replica::database>& db, sstring ks_name, sstring table_name, sstables::compaction_sstable_creator_fn creator) {
    auto all_jobs = co_await collect_all_shared_sstables(dir);
    auto destinations = co_await distribute_reshard_jobs(std::move(all_jobs));
    co_await run_resharding_jobs(dir, std::move(destinations), db, ks_name, table_name, std::move(creator));
}

future<sstables::generation_type>
highest_generation_seen(sharded<sstables::sstable_directory>& directory) {
    return directory.map_reduce0(std::mem_fn(&sstables::sstable_directory::highest_generation_seen), sstables::generation_from_value(0), [] (sstables::generation_type a, sstables::generation_type b) {
        return std::max(a, b);
    });
}

future<sstables::sstable::version_types>
highest_version_seen(sharded<sstables::sstable_directory>& dir, sstables::sstable_version_types system_version) {
    using version = sstables::sstable_version_types;
    return dir.map_reduce0(std::mem_fn(&sstables::sstable_directory::highest_version_seen), system_version, [] (version a, version b) {
        return std::max(a, b);
    });
}

future<>
distributed_loader::reshape(sharded<sstables::sstable_directory>& dir, sharded<replica::database>& db, sstables::reshape_mode mode,
        sstring ks_name, sstring table_name, sstables::compaction_sstable_creator_fn creator,
        std::function<bool (const sstables::shared_sstable&)> filter) {

    auto start = std::chrono::steady_clock::now();
    auto total_size = co_await dir.map_reduce0([&dir, &db, ks_name = std::move(ks_name), table_name = std::move(table_name), creator = std::move(creator), mode, filter] (sstables::sstable_directory& d) {
        auto& table = db.local().find_column_family(ks_name, table_name);
        auto& cm = db.local().get_compaction_manager();
        return d.reshape(cm, table, creator, mode, filter);
    }, uint64_t(0), std::plus<uint64_t>());

    if (total_size > 0) {
        auto duration = std::chrono::duration_cast<std::chrono::duration<float>>(std::chrono::steady_clock::now() - start);
        dblog.info("{}", fmt::format("Reshaped {} in {:.2f} seconds, {}", sstables::pretty_printed_data_size(total_size), duration.count(), sstables::pretty_printed_throughput(total_size, duration)));
    }
}

// Loads SSTables into the main directory (or staging) and returns how many were loaded
future<size_t>
distributed_loader::make_sstables_available(sstables::sstable_directory& dir, sharded<replica::database>& db,
        sharded<db::view::view_update_generator>& view_update_generator, fs::path datadir, sstring ks, sstring cf) {

    auto& table = db.local().find_column_family(ks, cf);
    auto new_sstables = std::vector<sstables::shared_sstable>();

    co_await dir.do_for_each_sstable([&table, datadir = std::move(datadir), &new_sstables] (sstables::shared_sstable sst) -> future<> {
        auto gen = table.calculate_generation_for_new_table();
        dblog.trace("Loading {} into {}, new generation {}", sst->get_filename(), datadir.native(), gen);
        co_await sst->move_to_new_dir(datadir.native(), gen, true);
            // When loading an imported sst, set level to 0 because it may overlap with existing ssts on higher levels.
            sst->set_sstable_level(0);
            new_sstables.push_back(std::move(sst));
    });

    // nothing loaded
    if (new_sstables.empty()) {
        co_return 0;
    }

    co_await table.add_sstables_and_update_cache(new_sstables).handle_exception([&table] (std::exception_ptr ep) {
        dblog.error("Failed to load SSTables for {}.{}: {}. Aborting.", table.schema()->ks_name(), table.schema()->cf_name(), ep);
        abort();
    });

    co_await coroutine::parallel_for_each(new_sstables, [&view_update_generator, &table] (sstables::shared_sstable sst) -> future<> {
        if (sst->requires_view_building()) {
            co_await view_update_generator.local().register_staging_sstable(sst, table.shared_from_this());
        }
    });

    co_return new_sstables.size();
}

future<>
distributed_loader::process_upload_dir(distributed<replica::database>& db, distributed<db::system_distributed_keyspace>& sys_dist_ks,
        distributed<db::view::view_update_generator>& view_update_generator, sstring ks, sstring cf) {
    seastar::thread_attributes attr;
    attr.sched_group = db.local().get_streaming_scheduling_group();

    return seastar::async(std::move(attr), [&db, &view_update_generator, &sys_dist_ks, ks = std::move(ks), cf = std::move(cf)] {
        global_column_family_ptr global_table(db, ks, cf);

        sharded<sstables::sstable_directory> directory;
        auto upload = fs::path(global_table->dir()) / sstables::upload_dir;
        directory.start(upload, service::get_local_streaming_priority(),
            db.local().get_config().initial_sstable_loading_concurrency(), std::ref(db.local().get_sharded_sst_dir_semaphore()),
            sstables::sstable_directory::need_mutate_level::yes,
            sstables::sstable_directory::lack_of_toc_fatal::no,
            sstables::sstable_directory::enable_dangerous_direct_import_of_cassandra_counters(db.local().get_config().enable_dangerous_direct_import_of_cassandra_counters()),
            sstables::sstable_directory::allow_loading_materialized_view::no,
            [&global_table] (fs::path dir, sstables::generation_type gen, sstables::sstable_version_types v, sstables::sstable_format_types f) {
                return global_table->make_sstable(dir.native(), gen, v, f, &error_handler_gen_for_upload_dir);

        }).get();

        auto stop = deferred_stop(directory);

        lock_table(directory, db, ks, cf).get();
        process_sstable_dir(directory).get();

        auto generation = highest_generation_seen(directory).get0();
        auto shard_generation_base = sstables::generation_value(generation) / smp::count + 1;

        // We still want to do our best to keep the generation numbers shard-friendly.
        // Each destination shard will manage its own generation counter.
        std::vector<std::atomic<int64_t>> shard_gen(smp::count);
        for (shard_id s = 0; s < smp::count; ++s) {
            shard_gen[s].store(shard_generation_base * smp::count + s, std::memory_order_relaxed);
        }

        reshard(directory, db, ks, cf, [&global_table, upload, &shard_gen] (shard_id shard) mutable {
            // we need generation calculated by instance of cf at requested shard
            auto gen = shard_gen[shard].fetch_add(smp::count, std::memory_order_relaxed);

            return global_table->make_sstable(upload.native(), sstables::generation_from_value(gen),
                    global_table->get_sstables_manager().get_highest_supported_format(),
                    sstables::sstable::format_types::big, &error_handler_gen_for_upload_dir);
        }).get();

        reshape(directory, db, sstables::reshape_mode::strict, ks, cf, [global_table, upload, &shard_gen] (shard_id shard) {
            auto gen = shard_gen[shard].fetch_add(smp::count, std::memory_order_relaxed);
            return global_table->make_sstable(upload.native(), sstables::generation_from_value(gen),
                  global_table->get_sstables_manager().get_highest_supported_format(),
                  sstables::sstable::format_types::big,
                  &error_handler_gen_for_upload_dir);
        }, sstables::sstable_directory::default_sstable_filter()).get();

        const bool use_view_update_path = db::view::check_needs_view_update_path(sys_dist_ks.local(), *global_table, streaming::stream_reason::repair).get0();

        auto datadir = upload.parent_path();
        if (use_view_update_path) {
            // Move to staging directory to avoid clashes with future uploads. Unique generation number ensures no collisions.
           datadir /= sstables::staging_dir;
        }

        size_t loaded = directory.map_reduce0([&db, ks, cf, datadir, &view_update_generator] (sstables::sstable_directory& dir) {
            return make_sstables_available(dir, db, view_update_generator, datadir, ks, cf);
        }, size_t(0), std::plus<size_t>()).get0();

        dblog.info("Loaded {} SSTables into {}", loaded, datadir.native());
    });
}

future<std::tuple<table_id, std::vector<std::vector<sstables::shared_sstable>>>>
distributed_loader::get_sstables_from_upload_dir(distributed<replica::database>& db, sstring ks, sstring cf) {
    return seastar::async([&db, ks = std::move(ks), cf = std::move(cf)] {
        global_column_family_ptr global_table(db, ks, cf);
        sharded<sstables::sstable_directory> directory;
        auto table_id = global_table->schema()->id();
        auto upload = fs::path(global_table->dir()) / sstables::upload_dir;

        directory.start(upload, service::get_local_streaming_priority(),
            db.local().get_config().initial_sstable_loading_concurrency(), std::ref(db.local().get_sharded_sst_dir_semaphore()),
            sstables::sstable_directory::need_mutate_level::yes,
            sstables::sstable_directory::lack_of_toc_fatal::no,
            sstables::sstable_directory::enable_dangerous_direct_import_of_cassandra_counters(db.local().get_config().enable_dangerous_direct_import_of_cassandra_counters()),
            sstables::sstable_directory::allow_loading_materialized_view::no,
            [&global_table] (fs::path dir, sstables::generation_type gen, sstables::sstable_version_types v, sstables::sstable_format_types f) {
                return global_table->make_sstable(dir.native(), gen, v, f, &error_handler_gen_for_upload_dir);

        }).get();

        auto stop = deferred_stop(directory);

        std::vector<std::vector<sstables::shared_sstable>> sstables_on_shards(smp::count);
        lock_table(directory, db, ks, cf).get();
        bool sort_sstables_according_to_owner = false;
        process_sstable_dir(directory, sort_sstables_according_to_owner).get();
        directory.invoke_on_all([&sstables_on_shards] (sstables::sstable_directory& d) mutable {
            sstables_on_shards[this_shard_id()] = d.get_unsorted_sstables();
        }).get();

        return std::make_tuple(table_id, std::move(sstables_on_shards));
    });
}

future<> distributed_loader::cleanup_column_family_temp_sst_dirs(sstring sstdir) {
    std::vector<future<>> futures;

    co_await lister::scan_dir(sstdir, { directory_entry_type::directory }, [&] (fs::path sstdir, directory_entry de) {
        // push futures that remove files/directories into an array of futures,
        // so that the supplied callback will not block scan_dir() from
        // reading the next entry in the directory.
        fs::path dirpath = sstdir / de.name;
        if (sstables::sstable::is_temp_dir(dirpath)) {
            dblog.info("Found temporary sstable directory: {}, removing", dirpath);
            futures.push_back(io_check([dirpath = std::move(dirpath)] () { return lister::rmdir(dirpath); }));
        }
        return make_ready_future<>();
    });

    co_await when_all_succeed(futures.begin(), futures.end()).discard_result();
}

future<> distributed_loader::handle_sstables_pending_delete(sstring pending_delete_dir) {
    std::vector<future<>> futures;

    co_await lister::scan_dir(pending_delete_dir, { directory_entry_type::regular }, [&futures] (fs::path dir, directory_entry de) {
        // push nested futures that remove files/directories into an array of futures,
        // so that the supplied callback will not block scan_dir() from
        // reading the next entry in the directory.
        fs::path file_path = dir / de.name;
        if (file_path.extension() == ".tmp") {
            dblog.info("Found temporary pending_delete log file: {}, deleting", file_path);
            futures.push_back(remove_file(file_path.string()));
        } else if (file_path.extension() == ".log") {
            dblog.info("Found pending_delete log file: {}, replaying", file_path);
            auto f = sstables::replay_pending_delete_log(file_path.string()).then([file_path = std::move(file_path)] {
                dblog.debug("Replayed {}, removing", file_path);
                return remove_file(file_path.string());
            });
            futures.push_back(std::move(f));
        } else {
            dblog.debug("Found unknown file in pending_delete directory: {}, ignoring", file_path);
        }
        return make_ready_future<>();
    });

    co_await when_all_succeed(futures.begin(), futures.end()).discard_result();
}

class table_population_metadata {
    distributed<replica::database>& _db;
    sstring _ks;
    sstring _cf;
    global_column_family_ptr _global_table;
    fs::path _base_path;
    std::unordered_map<sstring, lw_shared_ptr<sharded<sstables::sstable_directory>>> _sstable_directories;
    sstables::sstable_version_types _highest_version = sstables::oldest_writable_sstable_format;
    sstables::generation_type _highest_generation = sstables::generation_from_value(0);

public:
    table_population_metadata(distributed<replica::database>& db, sstring ks, sstring cf)
        : _db(db)
        , _ks(std::move(ks))
        , _cf(std::move(cf))
        , _global_table(_db, _ks, _cf)
        , _base_path(_global_table->dir())
    {}

    ~table_population_metadata() {
        // All directories must have been stopped
        // using table_population_metadata::stop()
        assert(_sstable_directories.empty());
    }

    future<> start() {
        assert(this_shard_id() == 0);
        for (auto subdir : { "", sstables::staging_dir, sstables::quarantine_dir }) {
            co_await start_subdir(subdir);
        }

        co_await smp::invoke_on_all([this] {
            _global_table->update_sstables_known_generation(_highest_generation);
            return _global_table->disable_auto_compaction();
        });
    }

    future<> stop() {
        for (auto it = _sstable_directories.begin(); it != _sstable_directories.end(); it = _sstable_directories.erase(it)) {
            co_await it->second->stop();
        }
    }

    fs::path get_path(std::string_view subdir) {
        return subdir.empty() ? _base_path : _base_path / subdir;
    }

    distributed<replica::database>& db() noexcept {
        return _db;
    }

    const sstring& ks() const noexcept {
        return _ks;
    }

    const sstring& cf() const noexcept {
        return _cf;
    }

    global_column_family_ptr& global_table() noexcept {
        return _global_table;
    };

    const global_column_family_ptr& global_table() const noexcept {
        return _global_table;
    };

    const std::unordered_map<sstring, lw_shared_ptr<sharded<sstables::sstable_directory>>>& sstable_directories() const noexcept {
        return _sstable_directories;
    }

    sstables::sstable::version_types highest_version() const noexcept {
        return _highest_version;
    }

    sstables::generation_type highest_generation() const noexcept {
        return _highest_generation;
    }

private:
    future<> start_subdir(sstring subdir);
};

future<> table_population_metadata::start_subdir(sstring subdir) {
    sstring sstdir = get_path(subdir).native();
    if (!co_await file_exists(sstdir)) {
        co_return;
    }

    // First pass, cleanup temporary sstable directories and sstables pending delete.
    co_await distributed_loader::cleanup_column_family_temp_sst_dirs(sstdir);
    auto pending_delete_dir = sstdir + "/" + sstables::sstable::pending_delete_dir_basename();
    auto exists = co_await file_exists(pending_delete_dir);
    if (exists) {
        co_await distributed_loader::handle_sstables_pending_delete(pending_delete_dir);
    }

    auto dptr = make_lw_shared<sharded<sstables::sstable_directory>>();
    auto& directory = *dptr;
    auto& global_table = _global_table;
    auto& db = _db;
    co_await directory.start(fs::path(sstdir), default_priority_class(),
        db.local().get_config().initial_sstable_loading_concurrency(), std::ref(db.local().get_sharded_sst_dir_semaphore()),
        sstables::sstable_directory::need_mutate_level::no,
        sstables::sstable_directory::lack_of_toc_fatal::yes,
        sstables::sstable_directory::enable_dangerous_direct_import_of_cassandra_counters(db.local().get_config().enable_dangerous_direct_import_of_cassandra_counters()),
        sstables::sstable_directory::allow_loading_materialized_view::yes,
        [&global_table] (fs::path dir, sstables::generation_type gen, sstables::sstable_version_types v, sstables::sstable_format_types f) {
            return global_table->make_sstable(dir.native(), gen, v, f);
    });

    // directory must be stopped using table_population_metadata::stop below
    _sstable_directories[subdir] = dptr;

    co_await distributed_loader::lock_table(directory, _db, _ks, _cf);
    co_await distributed_loader::process_sstable_dir(directory);

    // If we are resharding system tables before we can read them, we will not
    // know which is the highest format we support: this information is itself stored
    // in the system tables. In that case we'll rely on what we find on disk: we'll
    // at least not downgrade any files. If we already know that we support a higher
    // format than the one we see then we use that.
    auto sys_format = global_table->get_sstables_manager().get_highest_supported_format();
    auto sst_version = co_await highest_version_seen(directory, sys_format);
    auto generation = co_await highest_generation_seen(directory);

    _highest_version = std::max(sst_version, _highest_version);
    _highest_generation = std::max(generation, _highest_generation);
}

future<> distributed_loader::populate_column_family(table_population_metadata& metadata, sstring subdir, allow_offstrategy_compaction do_allow_offstrategy_compaction, must_exist dir_must_exist) {
    auto& db = metadata.db();
    const auto& ks = metadata.ks();
    const auto& cf = metadata.cf();
    auto sstdir = metadata.get_path(subdir).native();
    dblog.debug("Populating {}/{}/{} allow_offstrategy_compaction={} must_exist={}", ks, cf, sstdir, do_allow_offstrategy_compaction, dir_must_exist);

    assert(this_shard_id() == 0);

    if (!co_await file_exists(sstdir)) {
        if (dir_must_exist) {
            throw std::runtime_error(format("Populating {}/{} failed: {} does not exist", metadata.ks(), metadata.cf(), sstdir));
        }
        co_return;
    }

    auto& global_table = metadata.global_table();
    if (!metadata.sstable_directories().contains(subdir)) {
        dblog.error("Could not find sstables directory {}.{}/{}", ks, cf, subdir);
    }
    auto& directory = *metadata.sstable_directories().at(subdir);
    auto sst_version = metadata.highest_version();

    co_await reshard(directory, db, ks, cf, [&global_table, sstdir, sst_version] (shard_id shard) mutable {
        auto gen = smp::submit_to(shard, [&global_table] () {
            return global_table->calculate_generation_for_new_table();
        }).get0();

        return global_table->make_sstable(sstdir, gen, sst_version, sstables::sstable::format_types::big);
    });

    // The node is offline at this point so we are very lenient with what we consider
    // offstrategy.
    // SSTables created by repair may not conform to compaction strategy layout goal
    // because data segregation is only performed by compaction
    // Instead of reshaping them on boot, let's add them to maintenance set and allow
    // off-strategy compaction to reshape them. This will allow node to become online
    // ASAP. Given that SSTables with repair origin are disjoint, they can be efficiently
    // read from.
    auto eligible_for_reshape_on_boot = [] (const sstables::shared_sstable& sst) {
        return sst->get_origin() != sstables::repair_origin;
    };

    co_await reshape(directory, db, sstables::reshape_mode::relaxed, ks, cf, [global_table, sstdir, sst_version] (shard_id shard) {
        auto gen = global_table->calculate_generation_for_new_table();
        return global_table->make_sstable(sstdir, gen, sst_version, sstables::sstable::format_types::big);
    }, eligible_for_reshape_on_boot);

    co_await directory.invoke_on_all([global_table, &eligible_for_reshape_on_boot, do_allow_offstrategy_compaction] (sstables::sstable_directory& dir) -> future<> {
        co_await dir.do_for_each_sstable([&global_table, &eligible_for_reshape_on_boot, do_allow_offstrategy_compaction] (sstables::shared_sstable sst) {
            auto requires_offstrategy = sstables::offstrategy(do_allow_offstrategy_compaction && !eligible_for_reshape_on_boot(sst));
            return global_table->add_sstable_and_update_cache(sst, requires_offstrategy);
        });
        if (do_allow_offstrategy_compaction) {
            global_table->trigger_offstrategy_compaction();
        }
    });
}

future<> distributed_loader::populate_keyspace(distributed<replica::database>& db, sstring datadir, sstring ks_name) {
    auto ksdir = datadir + "/" + ks_name;
    auto& keyspaces = db.local().get_keyspaces();
    auto i = keyspaces.find(ks_name);
    if (i == keyspaces.end()) {
        dblog.warn("Skipping undefined keyspace: {}", ks_name);
        co_return;
    }

    dblog.info("Populating Keyspace {}", ks_name);
    auto& ks = i->second;
    auto& column_families = db.local().get_column_families();

    co_await coroutine::parallel_for_each(ks.metadata()->cf_meta_data() | boost::adaptors::map_values, [&] (schema_ptr s) -> future<> {
        auto uuid = s->id();
        lw_shared_ptr<replica::column_family> cf = column_families[uuid];
        sstring cfname = cf->schema()->cf_name();
        auto sstdir = ks.column_family_directory(ksdir, cfname, uuid);
        dblog.info("Keyspace {}: Reading CF {} id={} version={}", ks_name, cfname, uuid, s->version());

        auto metadata = table_population_metadata(db, ks_name, cfname);
        std::exception_ptr ex;

        try {
            co_await ks.make_directory_for_column_family(cfname, uuid);

            co_await metadata.start();
            co_await distributed_loader::populate_column_family(metadata, sstables::staging_dir, allow_offstrategy_compaction::no);
            co_await distributed_loader::populate_column_family(metadata, sstables::quarantine_dir, allow_offstrategy_compaction::no, must_exist::no);
            co_await distributed_loader::populate_column_family(metadata, "", allow_offstrategy_compaction::yes);
        } catch (...) {
            std::exception_ptr eptr = std::current_exception();
            std::string msg =
                format("Exception while populating keyspace '{}' with column family '{}' from file '{}': {}",
                        ks_name, cfname, sstdir, eptr);
            dblog.error("Exception while populating keyspace '{}' with column family '{}' from file '{}': {}",
                        ks_name, cfname, sstdir, eptr);
            try {
                std::rethrow_exception(eptr);
            } catch (sstables::compaction_stopped_exception& e) {
                // swallow compaction stopped exception, to allow clean shutdown.
            } catch (...) {
                ex = std::make_exception_ptr(std::runtime_error(msg.c_str()));
            }
        }

        co_await metadata.stop();
        if (ex) {
            co_await coroutine::return_exception_ptr(std::move(ex));
        }
    });
}

future<> distributed_loader::init_system_keyspace(sharded<db::system_keyspace>& sys_ks, distributed<replica::database>& db, distributed<service::storage_service>& ss, sharded<gms::gossiper>& g, db::config& cfg, db::table_selector& tables) {
    population_started = true;

    return seastar::async([&sys_ks, &db, &ss, &cfg, &g, &tables] {
        sys_ks.invoke_on_all([&db, &ss, &cfg, &g, &tables] (auto& sys_ks) {
            return sys_ks.make(db, ss, g, cfg, tables);
        }).get();

        const auto& cfg = db.local().get_config();
        for (auto& data_dir : cfg.data_file_directories()) {
            for (auto ksname : system_keyspaces) {
                if (!tables.contains_keyspace(ksname)) {
                    continue;
                }
                distributed_loader::populate_keyspace(db, data_dir, sstring(ksname)).get();
            }
        }

        db.invoke_on_all([&tables] (replica::database& db) {
            for (auto ksname : system_keyspaces) {
                if (!tables.contains_keyspace(ksname)) {
                    continue;
                }
                auto& ks = db.find_keyspace(ksname);
                for (auto& pair : ks.metadata()->cf_meta_data()) {
                    auto cfm = pair.second;
                    auto& cf = db.find_column_family(cfm);
                    cf.mark_ready_for_writes();
                }
                // for system keyspaces, we only do this post all population, and
                // only as a consistency measure.
                // change this if it is ever needed to sync system keyspace
                // population
                ks.mark_as_populated();
            }
            return make_ready_future<>();
        }).get();
    });
}

future<> distributed_loader::init_non_system_keyspaces(distributed<replica::database>& db,
        distributed<service::storage_proxy>& proxy, sharded<db::system_keyspace>& sys_ks) {
    return seastar::async([&db, &proxy, &sys_ks] {
        db.invoke_on_all([&proxy, &sys_ks] (replica::database& db) {
            return db.parse_system_tables(proxy, sys_ks);
        }).get();

        const auto& cfg = db.local().get_config();
        using ks_dirs = std::unordered_multimap<sstring, sstring>;

        ks_dirs dirs;

        parallel_for_each(cfg.data_file_directories(), [&db, &dirs] (sstring directory) {
            // we want to collect the directories first, so we can get a full set of potential dirs
            return lister::scan_dir(directory, { directory_entry_type::directory }, [&dirs] (fs::path datadir, directory_entry de) {
                if (!is_system_keyspace(de.name)) {
                    dirs.emplace(de.name, datadir.native());
                }
                return make_ready_future<>();
            });
        }).get();

        db.invoke_on_all([&dirs] (replica::database& db) {
            for (auto& [name, ks] : db.get_keyspaces()) {
                // mark all user keyspaces that are _not_ on disk as already
                // populated.
                if (!dirs.contains(ks.metadata()->name())) {
                    ks.mark_as_populated();
                }
            }
        }).get();

        for (bool prio_only : { true, false}) {
            std::vector<future<>> futures;

            // treat "dirs" as immutable to avoid modifying it while still in
            // a range-iteration. Also to simplify the "finally"
            for (auto i = dirs.begin(); i != dirs.end();) {
                auto& ks_name = i->first;
                auto j = i++;

                /**
                 * Must process in two phases: Prio and non-prio.
                 * This looks like it is not needed. And it is not
                 * in open-source version. But essential for enterprise.
                 * Do _not_ remove or refactor away.
                 */
                if (prio_only != is_load_prio_keyspace(ks_name)) {
                    continue;
                }

                auto e = dirs.equal_range(ks_name).second;
                // might have more than one dir for a keyspace iff data_file_directories is > 1 and
                // somehow someone placed sstables in more than one of them for a given ks. (import?)
                futures.emplace_back(parallel_for_each(j, e, [&](const std::pair<sstring, sstring>& p) {
                    auto& datadir = p.second;
                    return distributed_loader::populate_keyspace(db, datadir, ks_name);
                }).finally([&] {
                    return db.invoke_on_all([ks_name] (replica::database& db) {
                        // can be false if running test environment
                        // or ks_name was just a borked directory not representing
                        // a keyspace in schema tables.
                        if (db.has_keyspace(ks_name)) {
                            db.find_keyspace(ks_name).mark_as_populated();
                        }
                        return make_ready_future<>();
                    });
                }));
            }

            when_all_succeed(futures.begin(), futures.end()).discard_result().get();
        }

        db.invoke_on_all([] (replica::database& db) {
            return parallel_for_each(db.get_non_system_column_families(), [] (lw_shared_ptr<replica::table> table) {
                // Make sure this is called even if the table is empty
                table->mark_ready_for_writes();
                return make_ready_future<>();
            });
        }).get();
    });
}

}