example_snapshot_instant.cc

/************************************************************************
Copyright 2017-2019 eBay Inc.

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

    https://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 <libjungle/jungle.h>

// For removing directory purpose, not needed in practice.
#include "test_common.h"

using namespace jungle;

int main() {
    const static std::string path = "./db_example_snapshot";

    // Remove existing DB first.
    TestSuite::clearTestFile(path);

    // Initialize global resources with default config.
    jungle::init(GlobalConfig());

    // Open an instance at the given path, with default config.
    DB* db = nullptr;
    DB::open(&db, path, DBConfig());

    // Set {"hello", "world"} pair.
    db->set( KV("hello", "world") );

    // Open an instant snapshot without checkpoint marker.
    // The snapshot is based on the current DB image,
    // and will not persist after DB restarts.
    DB* snapshot = nullptr;
    db->openSnapshot(&snapshot);

    // Update - set {"hello", "WORLD"} pair.
    db->set( KV("hello", "WORLD") );

    // Search key "hello" in the latest DB instance,
    // should return the latest value "WORLD".
    SizedBuf value_out;
    Status s;
    s = db->get( SizedBuf("hello"), value_out );
    std::cout << "latest: return code " << s << ", "
              << value_out.toString() << std::endl;
    // Should free the memory of value after use.
    value_out.free();

    // Search key "hello" in the snapshot, should return "world".
    s = snapshot->get( SizedBuf("hello"), value_out );
    std::cout << "snapshot: return code " << s << ", "
              << value_out.toString() << std::endl;
    // Should free the memory of value after use.
    value_out.free();

    // Should close the snapshot handle first,
    // before closing the parent DB handle.
    DB::close(snapshot);
    DB::close(db);

    // Release global resources.
    jungle::shutdown();

    return 0;
}