Improve the performance of LevelDB in pika 4.0

[AlexStocks]

• 1 Expose the option parameters of LevelDB, where you can configure features like Bloom filters, etc., which may help improve read performance.

for example:

#include <iostream>
#include <leveldb/db.h>

int main() {
    leveldb::DB* db;
    leveldb::Options options;

    // Configure options
    options.create_if_missing = true;
    options.filter_policy = leveldb::NewBloomFilterPolicy(10); // Set Bloom filter with 10 bits per key

    // Open the database
    leveldb::Status status = leveldb::DB::Open(options, "/path/to/db", &db);

    if (status.ok()) {
        std::cout << "Database opened successfully!" << std::endl;

        // ... Your code to use the database ...

        delete db; // Remember to close and delete the database when done
    } else {
        std::cerr << "Failed to open the database: " << status.ToString() << std::endl;
    }

    return 0;
}