scylladb/compaction/time_window_compaction_strategy.cc

/*
 * Copyright (C) 2020-present ScyllaDB
 */

/*
 * SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.0
 */

#include "time_window_compaction_strategy.hh"
#include "mutation_writer/timestamp_based_splitting_writer.hh"
#include "mutation/mutation_source_metadata.hh"
#include "cql3/statements/property_definitions.hh"
#include "sstables/sstables.hh"
#include "sstables/sstable_set_impl.hh"
#include "compaction_strategy_state.hh"
#include "utils/error_injection.hh"

#include <seastar/util/lazy.hh>
#include <ranges>

namespace compaction {

extern logging::logger clogger;

using timestamp_type = api::timestamp_type;

time_window_compaction_strategy_state_ptr time_window_compaction_strategy::get_state(compaction_group_view& table_s) const {
    return table_s.get_compaction_strategy_state().get<time_window_compaction_strategy_state_ptr>();
}

const std::unordered_map<sstring, std::chrono::seconds> time_window_compaction_strategy_options::valid_window_units = {
        {"MINUTES", 60s}, {"HOURS", 3600s}, {"DAYS", 86400s}};

const std::unordered_map<sstring, time_window_compaction_strategy_options::timestamp_resolutions>
        time_window_compaction_strategy_options::valid_timestamp_resolutions = {
                {"MICROSECONDS", timestamp_resolutions::microsecond},
                {"MILLISECONDS", timestamp_resolutions::millisecond},
};

static std::chrono::seconds validate_compaction_window_unit(const std::map<sstring, sstring>& options) {
    std::chrono::seconds window_unit = time_window_compaction_strategy_options::DEFAULT_COMPACTION_WINDOW_UNIT;

    auto tmp_value = compaction_strategy_impl::get_value(options, time_window_compaction_strategy_options::COMPACTION_WINDOW_UNIT_KEY);
    if (tmp_value) {
        auto valid_window_units_it = time_window_compaction_strategy_options::valid_window_units.find(tmp_value.value());
        if (valid_window_units_it == time_window_compaction_strategy_options::valid_window_units.end()) {
            throw exceptions::configuration_exception(
                    fmt::format("Invalid window unit {} for {}", tmp_value.value(), time_window_compaction_strategy_options::COMPACTION_WINDOW_UNIT_KEY));
        }
        window_unit = valid_window_units_it->second;
    }

    return window_unit;
}

static std::chrono::seconds validate_compaction_window_unit(const std::map<sstring, sstring>& options, std::map<sstring, sstring>& unchecked_options) {
    auto window_unit = validate_compaction_window_unit(options);
    unchecked_options.erase(time_window_compaction_strategy_options::COMPACTION_WINDOW_UNIT_KEY);
    return window_unit;
}

static int validate_compaction_window_size(const std::map<sstring, sstring>& options) {
    auto tmp_value = compaction_strategy_impl::get_value(options, time_window_compaction_strategy_options::COMPACTION_WINDOW_SIZE_KEY);
    int window_size = cql3::statements::property_definitions::to_long(time_window_compaction_strategy_options::COMPACTION_WINDOW_SIZE_KEY, tmp_value,
            time_window_compaction_strategy_options::DEFAULT_COMPACTION_WINDOW_SIZE);

    if (window_size <= 0) {
        throw exceptions::configuration_exception(
                fmt::format("{} value ({}) must be greater than 1", time_window_compaction_strategy_options::COMPACTION_WINDOW_SIZE_KEY, window_size));
    }

    return window_size;
}

static int validate_compaction_window_size(const std::map<sstring, sstring>& options, std::map<sstring, sstring>& unchecked_options) {
    int window_size = validate_compaction_window_size(options);
    unchecked_options.erase(time_window_compaction_strategy_options::COMPACTION_WINDOW_SIZE_KEY);
    return window_size;
}

static db_clock::duration validate_expired_sstable_check_frequency_seconds(const std::map<sstring, sstring>& options) {
    db_clock::duration expired_sstable_check_frequency = time_window_compaction_strategy_options::DEFAULT_EXPIRED_SSTABLE_CHECK_FREQUENCY_SECONDS();

    auto tmp_value = compaction_strategy_impl::get_value(options, time_window_compaction_strategy_options::EXPIRED_SSTABLE_CHECK_FREQUENCY_SECONDS_KEY);
    if (tmp_value) {
        try {
            expired_sstable_check_frequency = std::chrono::seconds(std::stol(tmp_value.value()));
        } catch (const std::exception& e) {
            throw exceptions::syntax_exception(fmt::format(
                    "Invalid long value {} for {}", tmp_value.value(), time_window_compaction_strategy_options::EXPIRED_SSTABLE_CHECK_FREQUENCY_SECONDS_KEY));
        }
    }

    return expired_sstable_check_frequency;
}

static db_clock::duration validate_expired_sstable_check_frequency_seconds(
        const std::map<sstring, sstring>& options, std::map<sstring, sstring>& unchecked_options) {
    db_clock::duration expired_sstable_check_frequency = validate_expired_sstable_check_frequency_seconds(options);
    unchecked_options.erase(time_window_compaction_strategy_options::EXPIRED_SSTABLE_CHECK_FREQUENCY_SECONDS_KEY);
    return expired_sstable_check_frequency;
}

static time_window_compaction_strategy_options::timestamp_resolutions validate_timestamp_resolution(const std::map<sstring, sstring>& options) {
    time_window_compaction_strategy_options::timestamp_resolutions timestamp_resolution =
            time_window_compaction_strategy_options::timestamp_resolutions::microsecond;

    auto tmp_value = compaction_strategy_impl::get_value(options, time_window_compaction_strategy_options::TIMESTAMP_RESOLUTION_KEY);
    if (tmp_value) {
        if (!time_window_compaction_strategy_options::valid_timestamp_resolutions.contains(tmp_value.value())) {
            throw exceptions::configuration_exception(fmt::format(
                    "Invalid timestamp resolution {} for {}", tmp_value.value(), time_window_compaction_strategy_options::TIMESTAMP_RESOLUTION_KEY));
        } else {
            timestamp_resolution = time_window_compaction_strategy_options::valid_timestamp_resolutions.at(tmp_value.value());
        }
    }

    return timestamp_resolution;
}

static time_window_compaction_strategy_options::timestamp_resolutions validate_timestamp_resolution(
        const std::map<sstring, sstring>& options, std::map<sstring, sstring>& unchecked_options) {
    time_window_compaction_strategy_options::timestamp_resolutions timestamp_resolution = validate_timestamp_resolution(options);
    unchecked_options.erase(time_window_compaction_strategy_options::TIMESTAMP_RESOLUTION_KEY);
    return timestamp_resolution;
}

time_window_compaction_strategy_options::time_window_compaction_strategy_options(const std::map<sstring, sstring>& options) {
    auto window_unit = validate_compaction_window_unit(options);
    int window_size = validate_compaction_window_size(options);

    sstable_window_size = window_size * window_unit;
    expired_sstable_check_frequency = validate_expired_sstable_check_frequency_seconds(options);
    timestamp_resolution = validate_timestamp_resolution(options);

    auto it = options.find("enable_optimized_twcs_queries");
    if (it != options.end() && it->second == "false") {
        enable_optimized_twcs_queries = false;
    }
}

time_window_compaction_strategy_options::time_window_compaction_strategy_options(time_window_compaction_strategy_options&&) = default;

time_window_compaction_strategy_options::time_window_compaction_strategy_options(const time_window_compaction_strategy_options&) = default;

// options is a map of compaction strategy options and their values.
// unchecked_options is an analogical map from which already checked options are deleted.
// This helps making sure that only allowed options are being set.
void time_window_compaction_strategy_options::validate(const std::map<sstring, sstring>& options, std::map<sstring, sstring>& unchecked_options) {
    validate_compaction_window_unit(options, unchecked_options);
    validate_compaction_window_size(options, unchecked_options);
    validate_expired_sstable_check_frequency_seconds(options, unchecked_options);
    validate_timestamp_resolution(options, unchecked_options);
    compaction_strategy_impl::validate_min_max_threshold(options, unchecked_options);

    auto it = options.find("enable_optimized_twcs_queries");
    if (it != options.end() && it->second != "true" && it->second != "false") {
        throw exceptions::configuration_exception(fmt::format("enable_optimized_twcs_queries value ({}) must be \"true\" or \"false\"", it->second));
    }
    unchecked_options.erase("enable_optimized_twcs_queries");

    it = unchecked_options.find("unsafe_aggressive_sstable_expiration");
    if (it != unchecked_options.end()) {
        clogger.warn("unsafe_aggressive_sstable_expiration option is not supported for time window compaction strategy");
        unchecked_options.erase(it);
    }
}

class classify_by_timestamp {
    time_window_compaction_strategy_options _options;
    std::vector<int64_t> _known_windows;

public:
    explicit classify_by_timestamp(time_window_compaction_strategy_options options)
        : _options(std::move(options)) {
    }
    int64_t operator()(api::timestamp_type ts) {
        const auto window = time_window_compaction_strategy::get_window_for(_options, ts);
        if (const auto it = std::ranges::find(_known_windows, window); it != _known_windows.end()) {
            std::swap(*it, _known_windows.front());
            return window;
        }
        if (_known_windows.size() < time_window_compaction_strategy::max_data_segregation_window_count) {
            _known_windows.push_back(window);
            return window;
        }
        int64_t closest_window;
        int64_t min_diff = std::numeric_limits<int64_t>::max();
        for (const auto known_window : _known_windows) {
            if (const auto diff = std::abs(known_window - window); diff < min_diff) {
                min_diff = diff;
                closest_window = known_window;
            }
        }
        return closest_window;
    };
};

uint64_t time_window_compaction_strategy::adjust_partition_estimate(const mutation_source_metadata& ms_meta, uint64_t partition_estimate, schema_ptr s) const {
    // If not enough information, we assume the worst
    auto estimated_window_count = max_data_segregation_window_count;
    auto default_ttl = std::chrono::duration_cast<std::chrono::microseconds>(s->default_time_to_live());
    bool min_and_max_ts_available = ms_meta.min_timestamp && ms_meta.max_timestamp;
    auto estimate_window_count = [this](timestamp_type min_window, timestamp_type max_window) {
        const auto window_size = get_window_size(_options);
        return (max_window + (window_size - 1) - min_window) / window_size;
    };

    if (!min_and_max_ts_available && default_ttl.count()) {
        auto min_window = get_window_for(_options, timestamp_type(0));
        auto max_window = get_window_for(_options, timestamp_type(default_ttl.count()));

        estimated_window_count = estimate_window_count(min_window, max_window);
    } else if (min_and_max_ts_available) {
        auto min_window = get_window_for(_options, *ms_meta.min_timestamp);
        auto max_window = get_window_for(_options, *ms_meta.max_timestamp);

        estimated_window_count = estimate_window_count(min_window, max_window);
    }

    return partition_estimate / std::max(1UL, uint64_t(estimated_window_count));
}

mutation_reader_consumer time_window_compaction_strategy::make_interposer_consumer(
        const mutation_source_metadata& ms_meta, mutation_reader_consumer end_consumer) const {
    if (ms_meta.min_timestamp && ms_meta.max_timestamp &&
            get_window_for(_options, *ms_meta.min_timestamp) == get_window_for(_options, *ms_meta.max_timestamp)) {
        return end_consumer;
    }
    return [options = _options, end_consumer = std::move(end_consumer)](mutation_reader rd) mutable -> future<> {
        return mutation_writer::segregate_by_timestamp(std::move(rd), classify_by_timestamp(std::move(options)), end_consumer);
    };
}

compaction_descriptor time_window_compaction_strategy::get_reshaping_job(
        std::vector<sstables::shared_sstable> input, schema_ptr schema, reshape_config cfg) const {
    auto mode = cfg.mode;
    std::vector<sstables::shared_sstable> single_window;
    std::vector<sstables::shared_sstable> multi_window;

    size_t offstrategy_threshold = std::max(schema->min_compaction_threshold(), 4);
    size_t max_sstables = std::max(schema->max_compaction_threshold(), int(offstrategy_threshold));
    const uint64_t target_job_size = cfg.free_storage_space * reshape_target_space_overhead;

    if (mode == reshape_mode::relaxed) {
        offstrategy_threshold = max_sstables;
    }

    // Sort input sstables by first_key order
    // to allow efficient reshaping of disjoint sstables.
    std::sort(input.begin(), input.end(), [&schema](const sstables::shared_sstable& a, const sstables::shared_sstable& b) {
        return dht::ring_position(a->get_first_decorated_key()).less_compare(*schema, dht::ring_position(b->get_first_decorated_key()));
    });

    for (auto& sst : input) {
        auto min = sst->get_stats_metadata().min_timestamp;
        auto max = sst->get_stats_metadata().max_timestamp;
        if (get_window_for(_options, min) != get_window_for(_options, max)) {
            multi_window.push_back(sst);
        } else {
            single_window.push_back(sst);
        }
    }

    auto is_disjoint = [&schema, mode, max_sstables](const std::vector<sstables::shared_sstable>& ssts) {
        size_t tolerance = (mode == reshape_mode::relaxed) ? max_sstables : 0;
        return sstable_set_overlapping_count(schema, ssts) <= tolerance;
    };

    clogger.debug("time_window_compaction_strategy::get_reshaping_job: offstrategy_threshold={} max_sstables={} multi_window={} disjoint={} "
                  "single_window={} disjoint={}",
            offstrategy_threshold, max_sstables, multi_window.size(), seastar::value_of([&] {
                return !multi_window.empty() && sstable_set_overlapping_count(schema, multi_window) == 0;
            }),
            single_window.size(), seastar::value_of([&] {
                return !single_window.empty() && sstable_set_overlapping_count(schema, single_window) == 0;
            }));

    auto get_job_size = [](const std::vector<sstables::shared_sstable>& ssts) {
        return std::ranges::fold_left(ssts | std::views::transform(std::mem_fn(&sstables::sstable::bytes_on_disk)), uint64_t(0), std::plus{});
    };

    // Targets a space overhead of 10%. All disjoint sstables can be compacted together as long as they won't
    // cause an overhead above target. Otherwise, the job targets a maximum of #max_threshold sstables.
    auto need_trimming = [&](const std::vector<sstables::shared_sstable>& ssts, const uint64_t job_size, bool is_disjoint) {
        const size_t min_sstables = 2;
        auto is_above_target_size = job_size > target_job_size;

        return (ssts.size() > max_sstables && !is_disjoint) || (ssts.size() > min_sstables && is_above_target_size);
    };

    auto maybe_trim_job = [&need_trimming](std::vector<sstables::shared_sstable>& ssts, uint64_t job_size, bool is_disjoint) {
        while (need_trimming(ssts, job_size, is_disjoint)) {
            auto sst = ssts.back();
            ssts.pop_back();
            job_size -= sst->bytes_on_disk();
        }
    };

    if (!multi_window.empty()) {
        auto disjoint = is_disjoint(multi_window);
        auto job_size = get_job_size(multi_window);
        // Everything that spans multiple windows will need reshaping
        if (need_trimming(multi_window, job_size, disjoint)) {
            // When trimming, let's keep sstables with overlapping time window, so as to reduce write amplification.
            // For example, if there are N sstables spanning window W, where N <= 32, then we can produce all data for W
            // in a single compaction round, removing the need to later compact W to reduce its number of files.
            auto sort_size = std::min(max_sstables, multi_window.size());
            std::ranges::partial_sort(multi_window, multi_window.begin() + sort_size, std::ranges::less(), [](const sstables::shared_sstable& a) {
                return a->get_stats_metadata().max_timestamp;
            });
            maybe_trim_job(multi_window, job_size, disjoint);
        }
        compaction_descriptor desc(std::move(multi_window));
        desc.options = compaction_type_options::make_reshape();
        return desc;
    }

    // For things that don't span multiple windows, we compact windows that are individually too big
    auto all_disjoint = !single_window.empty() && is_disjoint(single_window);
    auto all_buckets = get_buckets(single_window, _options);
    single_window.clear();
    for (auto& [bucket, ssts] : all_buckets.first) {
        if (ssts.size() >= offstrategy_threshold) {
            clogger.debug("time_window_compaction_strategy::get_reshaping_job: bucket={} bucket_size={}", bucket, ssts.size());
            if (all_disjoint) {
                std::copy(ssts.begin(), ssts.end(), std::back_inserter(single_window));
                continue;
            }

            // reuse STCS reshape logic which will only compact similar-sized files, to increase overall efficiency
            // when reshaping time buckets containing a huge amount of files
            auto desc = size_tiered_compaction_strategy(_stcs_options).get_reshaping_job(std::move(ssts), schema, cfg);
            if (!desc.sstables.empty()) {
                return desc;
            }
        }
    }
    if (!single_window.empty()) {
        maybe_trim_job(single_window, get_job_size(single_window), all_disjoint);
        compaction_descriptor desc(std::move(single_window));
        desc.options = compaction_type_options::make_reshape();
        return desc;
    }

    return compaction_descriptor();
}

future<compaction_descriptor> time_window_compaction_strategy::get_sstables_for_compaction(compaction_group_view& table_s, strategy_control& control) {
    auto state = get_state(table_s);
    auto compaction_time = gc_clock::now();
    auto candidates = co_await control.candidates(table_s);

    if (candidates.empty()) {
        co_return compaction_descriptor();
    }

    auto now = db_clock::now();
    if (now - state->last_expired_check > _options.expired_sstable_check_frequency) {
        clogger.debug("[{}] TWCS expired check sufficiently far in the past, checking for fully expired SSTables", fmt::ptr(this));

        // Find fully expired SSTables. Those will be included no matter what.
        auto expired = table_s.fully_expired_sstables(candidates, compaction_time);
        if (!expired.empty()) {
            clogger.debug("[{}] Going to compact {} expired sstables", fmt::ptr(this), expired.size());
            co_return compaction_descriptor(has_only_fully_expired::yes, std::vector<sstables::shared_sstable>(expired.begin(), expired.end()));
        }
        // Keep checking for fully_expired_sstables until we don't find
        // any among the candidates, meaning they are either already compacted
        // or registered for compaction.
        state->last_expired_check = now;
    } else {
        clogger.debug("[{}] TWCS skipping check for fully expired SSTables", fmt::ptr(this));
    }

    co_await utils::get_local_injector().inject("twcs_get_sstables_for_compaction", utils::wait_for_message(30s));

    auto compaction_candidates = get_next_non_expired_sstables(table_s, control, std::move(candidates), compaction_time, *state);
    clogger.debug("[{}] Going to compact {} non-expired sstables", fmt::ptr(this), compaction_candidates.size());
    co_return compaction_descriptor(std::move(compaction_candidates));
}

time_window_compaction_strategy::bucket_compaction_mode time_window_compaction_strategy::compaction_mode(
        const time_window_compaction_strategy_state& state, const bucket_t& bucket, timestamp_type bucket_key, timestamp_type now, size_t min_threshold) const {
    // STCS will also be performed on older window buckets, to avoid a bad write and
    // space amplification when something like read repair cause small updates to
    // those past windows.

    if (bucket.size() >= 2 && !is_last_active_bucket(bucket_key, now) && state.recent_active_windows.contains(bucket_key)) {
        return bucket_compaction_mode::major;
    } else if (bucket.size() >= size_t(min_threshold)) {
        return bucket_compaction_mode::size_tiered;
    }
    return bucket_compaction_mode::none;
}

std::vector<sstables::shared_sstable> time_window_compaction_strategy::get_next_non_expired_sstables(compaction_group_view& table_s, strategy_control& control,
        std::vector<sstables::shared_sstable> non_expiring_sstables, gc_clock::time_point compaction_time, time_window_compaction_strategy_state& state) {
    auto most_interesting = get_compaction_candidates(table_s, control, non_expiring_sstables, state);

    if (!most_interesting.empty()) {
        return most_interesting;
    }

    if (!table_s.tombstone_gc_enabled()) {
        return {};
    }

    // if there is no sstable to compact in standard way, try compacting single sstable whose droppable tombstone
    // ratio is greater than threshold.
    std::erase_if(non_expiring_sstables, [this, compaction_time, &table_s](const sstables::shared_sstable& sst) -> bool {
        return !worth_dropping_tombstones(sst, compaction_time, table_s);
    });
    if (non_expiring_sstables.empty()) {
        return {};
    }
    auto it = std::ranges::min_element(non_expiring_sstables, [](auto& i, auto& j) {
        return i->get_stats_metadata().min_timestamp < j->get_stats_metadata().min_timestamp;
    });
    return {*it};
}

std::vector<sstables::shared_sstable> time_window_compaction_strategy::get_compaction_candidates(compaction_group_view& table_s, strategy_control& control,
        std::vector<sstables::shared_sstable> candidate_sstables, time_window_compaction_strategy_state& state) {
    auto [buckets, max_timestamp] = get_buckets(std::move(candidate_sstables), _options);
    // Update the highest window seen, if necessary
    state.highest_window_seen = std::max(state.highest_window_seen, max_timestamp);

    return newest_bucket(table_s, control, std::move(buckets), table_s.min_compaction_threshold(), table_s.schema()->max_compaction_threshold(),
            state.highest_window_seen, state);
}

timestamp_type time_window_compaction_strategy::get_window_lower_bound(std::chrono::seconds sstable_window_size, timestamp_type timestamp) {
    using namespace std::chrono;
    // mask out window size from timestamp to get lower bound of its window
    auto num_windows = microseconds(timestamp) / sstable_window_size;

    return duration_cast<microseconds>(num_windows * sstable_window_size).count();
}

std::pair<std::map<timestamp_type, std::vector<sstables::shared_sstable>>, timestamp_type> time_window_compaction_strategy::get_buckets(
        std::vector<sstables::shared_sstable> files, const time_window_compaction_strategy_options& options) {
    std::map<timestamp_type, std::vector<sstables::shared_sstable>> buckets;

    timestamp_type max_timestamp = 0;
    // Create map to represent buckets
    // For each sstable, add sstable to the time bucket
    // Where the bucket is the file's max timestamp rounded to the nearest window bucket
    for (auto&& f : files) {
        timestamp_type ts = to_timestamp_type(options.timestamp_resolution, f->get_stats_metadata().max_timestamp);
        timestamp_type lower_bound = get_window_lower_bound(options.sstable_window_size, ts);
        buckets[lower_bound].push_back(std::move(f));
        max_timestamp = std::max(max_timestamp, lower_bound);
    }

    return std::make_pair(std::move(buckets), max_timestamp);
}

} // namespace compaction

template <>
struct fmt::formatter<std::map<compaction::timestamp_type, std::vector<sstables::shared_sstable>>> {
    constexpr auto parse(format_parse_context& ctx) {
        return ctx.begin();
    }
    auto format(const std::map<compaction::timestamp_type, std::vector<sstables::shared_sstable>>& buckets, fmt::format_context& ctx) const {
        auto out = fmt::format_to(ctx.out(), "  buckets = {{\n");
        for (auto& [timestamp, sstables] : buckets | std::views::reverse) {
            out = fmt::format_to(out, "    key={}, size={}\n", timestamp, sstables.size());
        }
        return fmt::format_to(out, "  }}\n");
    }
};

namespace compaction {

std::vector<sstables::shared_sstable> time_window_compaction_strategy::newest_bucket(compaction_group_view& table_s, strategy_control& control,
        std::map<timestamp_type, std::vector<sstables::shared_sstable>> buckets, int min_threshold, int max_threshold, timestamp_type now,
        time_window_compaction_strategy_state& state) {
    clogger.debug("time_window_compaction_strategy::newest_bucket:\n  now {}\n{}", now, buckets);

    for (auto&& [key, bucket] : buckets | std::views::reverse) {
        bool last_active_bucket = is_last_active_bucket(key, now);
        if (last_active_bucket) {
            state.recent_active_windows.insert(key);
        }
        switch (compaction_mode(state, bucket, key, now, min_threshold)) {
        case bucket_compaction_mode::size_tiered: {
            // If we're in the newest bucket, we'll use STCS to prioritize sstables.
            auto stcs_interesting_bucket = size_tiered_compaction_strategy::most_interesting_bucket(bucket, min_threshold, max_threshold, _stcs_options);

            // If the tables in the current bucket aren't eligible in the STCS strategy, we'll skip it and look for other buckets
            if (!stcs_interesting_bucket.empty()) {
                clogger.debug("bucket size {} >= 2, key {}, performing STCS on what's here", bucket.size(), key);
                return stcs_interesting_bucket;
            }
            break;
        }
        case bucket_compaction_mode::major:
            // serializes per-window major on a past window, to avoid missing its files being currently compacted.
            if (control.has_ongoing_compaction(table_s)) {
                break;
            }
            clogger.debug("bucket size {} >= 2 and not in current bucket, key {}, compacting what's here", bucket.size(), key);
            return trim_to_threshold(std::move(bucket), max_threshold);
        default:
            // windows needing major will remain with major state until they're compacted into one file.
            // after that, they will fall into default mode where we'll stop considering them as a recent window
            // which needs major. That's to avoid terrible writeamp as streaming may push data into older windows.
            if (!last_active_bucket) {
                state.recent_active_windows.erase(key);
            }
            clogger.debug("No compaction necessary for bucket size {} , key {}, now {}", bucket.size(), key, now);
            break;
        }
    }
    return {};
}

std::vector<sstables::shared_sstable> time_window_compaction_strategy::trim_to_threshold(std::vector<sstables::shared_sstable> bucket, int max_threshold) {
    auto n = std::min(bucket.size(), size_t(max_threshold));
    // Trim the largest sstables off the end to meet the maxThreshold
    std::ranges::partial_sort(bucket, bucket.begin() + n, std::ranges::less(), std::mem_fn(&sstables::sstable::ondisk_data_size));
    bucket.resize(n);
    return bucket;
}

future<int64_t> time_window_compaction_strategy::estimated_pending_compactions(compaction_group_view& table_s) const {
    auto state = get_state(table_s);
    auto min_threshold = table_s.min_compaction_threshold();
    auto max_threshold = table_s.schema()->max_compaction_threshold();
    auto main_set = co_await table_s.main_sstable_set();
    auto candidate_sstables = *main_set->all() | std::ranges::to<std::vector>();
    auto [buckets, max_timestamp] = get_buckets(std::move(candidate_sstables), _options);

    int64_t n = 0;
    for (auto& [bucket_key, bucket] : buckets) {
        switch (compaction_mode(*state, bucket, bucket_key, max_timestamp, min_threshold)) {
        case bucket_compaction_mode::size_tiered:
            n += size_tiered_compaction_strategy::estimated_pending_compactions(bucket, min_threshold, max_threshold, _stcs_options);
            break;
        case bucket_compaction_mode::major:
            n++;
            break;
        default:
            break;
        }
    }
    co_return n;
}

std::vector<compaction_descriptor> time_window_compaction_strategy::get_cleanup_compaction_jobs(
        compaction_group_view& table_s, std::vector<sstables::shared_sstable> candidates) const {
    std::vector<compaction_descriptor> ret;
    for (auto&& [_, sstables] : get_buckets(std::move(candidates), _options).first) {
        auto per_window_jobs = size_tiered_compaction_strategy(_stcs_options).get_cleanup_compaction_jobs(table_s, std::move(sstables));
        std::move(per_window_jobs.begin(), per_window_jobs.end(), std::back_inserter(ret));
    }
    return ret;
}

std::unique_ptr<sstables::sstable_set_impl> time_window_compaction_strategy::make_sstable_set(const compaction_group_view& ts) const {
    return std::make_unique<sstables::time_series_sstable_set>(ts.schema(), _options.enable_optimized_twcs_queries);
}

} // namespace compaction