be/src/olap/schema_cache.h

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

#include <fmt/core.h>
#include <parallel_hashmap/phmap.h>

#include <algorithm>
#include <memory>
#include <mutex>
#include <type_traits>
#include <vector>

#include "common/logging.h"
#include "olap/iterators.h"
#include "olap/olap_common.h"
#include "olap/schema.h"
#include "olap/tablet.h"
#include "olap/tablet_schema.h"
#include "util/time.h"

namespace doris {

namespace segment_v2 {
class Segment;
class SegmentIterator;
using SegmentIteratorUPtr = std::unique_ptr<SegmentIterator>;
} // namespace segment_v2

// The SchemaCache is utilized to cache pre-allocated data structures,
// eliminating the need for frequent allocation and deallocation during usage.
// This caching mechanism proves immensely advantageous, particularly in scenarios
// with high concurrency, where queries are executed simultaneously.
class SchemaCache : public LRUCachePolicy {
public:
    static SchemaCache* instance();

    static void create_global_instance(size_t capacity);

    static std::string get_schema_key(int64_t tablet_id, const std::vector<TColumn>& columns,
                                      int32_t version);

    // Get a shared cached schema from cache, schema_key is a subset of column unique ids
    TabletSchemaSPtr get_schema(const std::string& schema_key) {
        if (!instance() || schema_key.empty()) {
            return {};
        }
        auto* lru_handle = lookup(schema_key);
        if (lru_handle) {
            Defer release([cache = this, lru_handle] { cache->release(lru_handle); });
            auto* value = (CacheValue*)LRUCachePolicy::value(lru_handle);
            VLOG_DEBUG << "use cache schema";
            return value->tablet_schema;
        }
        return {};
    }

    // Insert a shared Schema into cache, schema_key is full column unique ids
    void insert_schema(const std::string& key, TabletSchemaSPtr schema) {
        if (!instance() || key.empty()) {
            return;
        }
        auto* value = new CacheValue;
        value->tablet_schema = schema;

        auto* lru_handle = insert(key, value, 1, schema->mem_size(), CachePriority::NORMAL);
        release(lru_handle);
    }

    class CacheValue : public LRUCacheValueBase {
    public:
        TabletSchemaSPtr tablet_schema = nullptr;
    };

    SchemaCache(size_t capacity)
            : LRUCachePolicy(CachePolicy::CacheType::SCHEMA_CACHE, capacity, LRUCacheType::NUMBER,
                             config::schema_cache_sweep_time_sec) {}

private:
    static constexpr char SCHEMA_DELIMITER = '-';
};

} // namespace doris