ClickHouse/src/Storages/LiveView/StorageLiveView.h

#pragma once
/* Copyright (c) 2018 BlackBerry Limited

Licensed 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 <Storages/IStorage.h>
#include <Core/BackgroundSchedulePool.h>

#include <mutex>
#include <condition_variable>


namespace DB
{


struct BlocksMetadata
{
    String hash;
    UInt64 version;
    std::chrono::time_point<std::chrono::system_clock> time;
};

struct MergeableBlocks
{
    BlocksPtrs blocks;
    Block sample_block;
};

class IAST;
using ASTPtr = std::shared_ptr<IAST>;
using BlocksMetadataPtr = std::shared_ptr<BlocksMetadata>;
using MergeableBlocksPtr = std::shared_ptr<MergeableBlocks>;

class Pipe;
using Pipes = std::vector<Pipe>;


class StorageLiveView final : public IStorage, WithContext
{
friend class LiveViewSource;
friend class LiveViewEventsSource;
friend class LiveViewSink;

using Time = std::chrono::time_point<std::chrono::system_clock>;
using Seconds = std::chrono::seconds;
using MilliSeconds = std::chrono::milliseconds;

public:
    StorageLiveView(
        const StorageID & table_id_,
        ContextPtr context_,
        const ASTCreateQuery & query,
        const ColumnsDescription & columns,
        const String & comment);

    ~StorageLiveView() override;

    String getName() const override { return "LiveView"; }

    bool isView() const override { return true; }

    /// It is passed inside the query and solved at its level.
    bool supportsSampling() const override { return true; }

    bool supportsFinal() const override { return true; }

    NamesAndTypesList getVirtuals() const override;

    void checkTableCanBeDropped([[ maybe_unused ]] ContextPtr query_context) const override;

    void drop() override;

    void startup() override;

    void shutdown() override;

    Pipe read(
        const Names & column_names,
        const StorageSnapshotPtr & storage_snapshot,
        SelectQueryInfo & query_info,
        ContextPtr context,
        QueryProcessingStage::Enum processed_stage,
        size_t max_block_size,
        size_t num_streams) override;

    Pipe watch(
        const Names & column_names,
        const SelectQueryInfo & query_info,
        ContextPtr context,
        QueryProcessingStage::Enum & processed_stage,
        size_t max_block_size,
        size_t num_streams) override;

    ASTPtr getInnerQuery() const { return select_query_description.select_query->clone(); }

    /// Get blocks hash
    /// must be called with mutex locked
    String getBlocksHashKey(const std::lock_guard<std::mutex> &)
    {
        if (*blocks_metadata_ptr)
            return (*blocks_metadata_ptr)->hash;
        return {};
    }
    /// Get blocks version
    /// must be called with mutex locked
    UInt64 getBlocksVersion(const std::lock_guard<std::mutex> &)
    {
        if (*blocks_metadata_ptr)
            return (*blocks_metadata_ptr)->version;
        return 0;
    }

    void writeBlock(const Block & block, ContextPtr context);

    void refresh();

private:
    void refreshImpl(const std::lock_guard<std::mutex> & lock);

    String getBlocksTableName() const
    {
        return getStorageID().table_name + "_blocks";
    }

    Block getHeader() const;

    StoragePtr getDependentTableStorage() const;

    ASTPtr getInnerBlocksQuery();

    /// Check we have any active readers
    /// must be called with mutex locked
    bool hasActiveUsers(const std::lock_guard<std::mutex> &) const
    {
        return active_ptr.use_count() > 1;
    }

    /// Get blocks time
    /// must be called with mutex locked
    Time getBlocksTime(const std::lock_guard<std::mutex> &)
    {
        if (*blocks_metadata_ptr)
            return (*blocks_metadata_ptr)->time;
        return {};
    }

    /// Reset blocks
    /// must be called with mutex locked
    void reset(const std::lock_guard<std::mutex> &)
    {
        (*blocks_ptr).reset();
        if (*blocks_metadata_ptr)
            (*blocks_metadata_ptr)->hash.clear();
        mergeable_blocks.reset();
    }

    /// Collect mergeable blocks and their sample. Must be called holding mutex
    MergeableBlocksPtr collectMergeableBlocks(ContextPtr context, const std::lock_guard<std::mutex> & lock) const;

    /// Complete query using input streams from mergeable blocks
    QueryPipelineBuilder completeQuery(Pipes pipes);

    /// Read new data blocks that store query result
    bool getNewBlocks(const std::lock_guard<std::mutex> & lock);

    void periodicRefreshTaskFunc();

    /// Must be called with mutex locked
    void scheduleNextPeriodicRefresh(const std::lock_guard<std::mutex> & lock);

    SelectQueryDescription select_query_description;

    /// Query over the mergeable blocks to produce final result
    ASTPtr inner_blocks_query;

    ContextMutablePtr live_view_context;

    Poco::Logger * log;

    bool is_periodically_refreshed = false;
    Seconds periodic_live_view_refresh;

    /// Mutex to protect access to sample block and inner_blocks_query
    mutable std::mutex sample_block_lock;
    mutable Block sample_block;

    /// Mutex for the blocks and ready condition
    std::mutex mutex;
    /// New blocks ready condition to broadcast to readers
    /// that new blocks are available
    std::condition_variable condition;

    /// Active users
    std::shared_ptr<bool> active_ptr;
    /// Current data blocks that store query result
    std::shared_ptr<BlocksPtr> blocks_ptr;
    /// Current data blocks metadata
    std::shared_ptr<BlocksMetadataPtr> blocks_metadata_ptr;
    MergeableBlocksPtr mergeable_blocks;

    std::atomic<bool> shutdown_called = false;

    /// Periodic refresh task used when [PERIODIC] REFRESH is specified in create statement
    BackgroundSchedulePool::TaskHolder periodic_refresh_task;
};

}