querycache.cpp

/*
    SPDX-FileCopyrightText: 2012 Volker Krause <vkrause@kde.org>
 
    SPDX-License-Identifier: LGPL-2.0-or-later
 */
 
#include "querycache.h"
#include "datastore.h"
#include "dbtype.h"
 
#include <QHash>
#include <QSqlDriver>
#include <QSqlQuery>
#include <QThreadStorage>
#include <QTimer>
 
#include <chrono>
#include <list>
 
using namespace std::chrono_literals;
using namespace Akonadi;
using namespace Akonadi::Server;
 
namespace
{
// After these seconds without activity the cache is cleaned
constexpr auto CleanupTimeout = 60s;
constexpr int MaxCacheSize = 50;
 
/// LRU cache with limited size and auto-cleanup after given
/// period of time
class Cache
{
public:
    Cache()
    {
        QObject::connect(&m_cleanupTimer, &QTimer::timeout, &m_cleanupTimer, std::bind(&Cache::cleanup, this));
        m_cleanupTimer.setSingleShot(true);
    }
 
    std::optional<QSqlQuery> query(const QString &queryStatement)
    {
        m_cleanupTimer.start(CleanupTimeout);
        auto it = m_keys.find(queryStatement);
        if (it == m_keys.end()) {
            return {};
        }
 
        auto query = std::move(it->second->query);
        m_queries.erase(it->second);
        m_keys.erase(it);
 
        return query;
    }
 
    void insert(const QString &queryStatement, QSqlQuery query)
    {
        if (m_queries.size() >= MaxCacheSize) {
            // Get the last entry in m_queries
            auto query_it = std::prev(m_queries.end());
            // Find and erase corresponding entry in m_keys
            std::erase_if(m_keys, [&](const auto &node) {
                return node.second == query_it;
            });
            // Remove the last entry from m_queries, making room for a new one.
            m_queries.pop_back();
        }
 
        m_queries.emplace_front(std::move(query));
        m_keys.emplace(queryStatement, m_queries.begin());
    }
 
    void cleanup()
    {
        m_keys.clear();
        m_queries.clear();
    }
 
public: // public, this is just a helper class
    struct Node {
        QSqlQuery query;
    };
    std::list<Node> m_queries;
    std::unordered_map<QString, std::list<Node>::iterator> m_keys;
    QTimer m_cleanupTimer;
};
 
QThreadStorage<Cache *> g_queryCache;
 
Cache *perThreadCache()
{
    if (!g_queryCache.hasLocalData()) {
        g_queryCache.setLocalData(new Cache());
    }
 
    return g_queryCache.localData();
}
 
} // namespace
 
std::optional<QSqlQuery> QueryCache::query(const QString &queryStatement)
{
    return perThreadCache()->query(queryStatement);
}
 
void QueryCache::insert(const QSqlDatabase &db, const QString &queryStatement, QSqlQuery query)
{
    if (DbType::type(db) != DbType::Sqlite) {
        perThreadCache()->insert(queryStatement, std::move(query));
    }
}
 
void QueryCache::clear()
{
    if (!g_queryCache.hasLocalData()) {
        return;
    }
 
    g_queryCache.localData()->cleanup();
}
 
size_t QueryCache::capacity()
{
    return MaxCacheSize;
}