// Open a db with default options.
            HaloDBOptions options = new HaloDBOptions();
    
            // Size of each data file will be 1GB.
            options.setMaxFileSize(1024 * 1024 * 1024);

            // Size of each tombstone file will be 64MB
            // Large file size mean less file count but will slow down db open time. But if set
            // file size too small, it will result large amount of tombstone files under db folder
            options.setMaxTombstoneFileSize(64 * 1024 * 1024);

            // Set the number of threads used to scan index and tombstone files in parallel
            // to build in-memory index during db open. It must be a positive number which is
            // not greater than Runtime.getRuntime().availableProcessors().
            // It is used to speed up db open time.
            options.setBuildIndexThreads(8);

            // The threshold at which page cache is synced to disk.
            // data will be durable only if it is flushed to disk, therefore
            // more data will be lost if this value is set too high. Setting
            // this value too low might interfere with read and write performance.
            options.setFlushDataSizeBytes(10 * 1024 * 1024);
    
            // The percentage of stale data in a data file at which the file will be compacted.
            // This value helps control write and space amplification. Increasing this value will
            // reduce write amplification but will increase space amplification.
            // This along with the compactionJobRate below is the most important setting
            // for tuning HaloDB performance. If this is set to x then write amplification 
            // will be approximately 1/x. 
            options.setCompactionThresholdPerFile(0.7);
    
            // Controls how fast the compaction job should run.
            // This is the amount of data which will be copied by the compaction thread per second.
            // Optimal value depends on the compactionThresholdPerFile option.
            options.setCompactionJobRate(50 * 1024 * 1024);
    
            // Setting this value is important as it helps to preallocate enough
            // memory for the off-heap cache. If the value is too low the db might
            // need to rehash the cache. For a db of size n set this value to 2*n.
            options.setNumberOfRecords(100_000_000);
            
            // Delete operation for a key will write a tombstone record to a tombstone file.
            // the tombstone record can be removed only when all previous version of that key
            // has been deleted by the compaction job.
            // enabling this option will delete during startup all tombstone records whose previous
            // versions were removed from the data file.
            options.setCleanUpTombstonesDuringOpen(true);
    
            // HaloDB does native memory allocation for the in-memory index.
            // Enabling this option will release all allocated memory back to the kernel when the db is closed.
            // This option is not necessary if the JVM is shutdown when the db is closed, as in that case
            // allocated memory is released automatically by the kernel.
            // If using in-memory index without memory pool this option,
            // depending on the number of records in the database,
            // could be a slow as we need to call _free_ for each record.
            options.setCleanUpInMemoryIndexOnClose(false);
            
            // ** settings for memory pool **
            options.setUseMemoryPool(true);
    
            // Hash table implementation in HaloDB is similar to that of ConcurrentHashMap in Java 7.
            // Hash table is divided into segments and each segment manages its own native memory.
            // The number of segments is twice the number of cores in the machine.
            // A segment's memory is further divided into chunks whose size can be configured here. 
            options.setMemoryPoolChunkSize(2 * 1024 * 1024);
    
            // using a memory pool requires us to declare the size of keys in advance.
            // Any write request with key length greater than the declared value will fail, but it
            // is still possible to store keys smaller than this declared size. 
            options.setFixedKeySize(8);
    
            // Represents a database instance and provides all methods for operating on the database.
            HaloDB db = null;
    
            // The directory will be created if it doesn't exist and all database files will be stored in this directory
            String directory = "directory";
    
            // Open the database. Directory will be created if it doesn't exist.
            // If we are opening an existing database HaloDB needs to scan all the
            // index files to create the in-memory index, which, depending on the db size, might take a few minutes.
            db = HaloDB.open(directory, options);
    
            // key and values are byte arrays. Key size is restricted to 128 bytes.
            byte[] key1 = Ints.toByteArray(200);
            byte[] value1 = "Value for key 1".getBytes();
    
            byte[] key2 = Ints.toByteArray(300);
            byte[] value2 = "Value for key 2".getBytes();
    
            // add the key-value pair to the database.
            db.put(key1, value1);
            db.put(key2, value2);
    
            // read the value from the database.
            value1 = db.get(key1);
            value2 = db.get(key2);
    
            // delete a key from the database.
            db.delete(key1);
    
            // Open an iterator and iterate through all the key-value records.
            HaloDBIterator iterator = db.newIterator();
            while (iterator.hasNext()) {
                Record record = iterator.next();
                System.out.println(Ints.fromByteArray(record.getKey()));
                System.out.println(new String(record.getValue()));
            }
    
            // get stats and print it.
            HaloDBStats stats = db.stats();
            System.out.println(stats.toString());
    
            // reset stats
            db.resetStats();
            
            // pause background compaction thread.
            // if a file is being compacted the thread
            // will block until the compaction is complete.
            db.pauseCompaction();
            
            // resume background compaction thread.
            db.resumeCompaction();
            
            // repeatedly calling pause/resume compaction methods will have no effect.

            // Close the database.
            db.close();