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Build and Run

To build:

$ cd ~/bank && make

To start the server. By default the server listens at 127.0.0.1:7890.

$ cd ~/bank && src/bank &

Start a client session with nc. Please note that lines starting with "200" or "210" are server responses.

$ nc localhost 7890
OPEN
200 - ACCOUNT NUMBER 1
DEPOSIT 100 TO 1
200 - OLD AMOUNT 0 NEW AMOUNT 100
WITHDRAW 50 FROM 1
200 - OLD AMOUNT 100 NEW AMOUNT 50
OPEN
200 - ACCOUNT NUMBER 2
TRANSFER 50 FROM 1 TO 2
200 - OLD AMOUNT 50 NEW AMOUNT 0
HISTORY 1
210 - CURRENT 0
210 - AT 1455036422 TRANSFERRED 50 TO 2
210 - AT 1455036402 WITHDREW 50
210 - AT 1455036379 DEPOSITED 100
210 - AT 1455036364 OPENED
210 -

Server command options:

Usage: bank [ -r root_dir ] [ -a addr ] [ -p port ] [ -v ] [ -h ]
            [ -s wal_block_size ] [ -d max_lsn_drift ]
            [ -b user_hash_bits ]

    -r  set db root dir to <root_dir>, default is "."
    -a  bind to address <addr>, default is "127.0.0.1"
    -p  bind to port <port>, default is "7890"
    -s, -d, -b  don't use, testing only
    -v  verbose output
    -h  print this message and quit

Assumption for Durability

Durability is implemented using WAL (write ahead log). To ensure a consistent WAL, the disk IO must satisfy the following:

  • Writing to a hard disk sector must be atomic. A sector write either succeeded or did never happen.

  • Appending to a file must be sequential. A later append cannot write to disk before a former append does.

Tests

To run automated testing:

$ cd ~/bank && make test

The automated tests include:

  • functional test
  • durability test
  • concurrency test

The durability test is done by starting the server with an older version of the database file, then check that all missed transactions are restored.

Performance

Disk IO is slow. Batched (delayed) appending of WAL file is used to improve system throughput, at the expense of slightly slowing down each individual transaction.

One the AWS server, the system throughput can reach 9989.16 transactions per second with default options.

Future Improvements

  1. security -- currently no authentication nor authorization,
  2. asyncio
  3. dynamically resizing user hash table based on number of conflicts,
  4. user session control -- timeout connection and etc,
  5. WAL rotation