Unfortunatly, this DB can't create new tables yet. Therefore, to use this DB, you need to create in /tmp/simpledb at least 2 files: tableName.meta and tableName.data.
In tableName.meta you must write scheme of tableName, for example:
id;int
name;varchar;10
dt;datetime
You can run python3 createdb.py or python3 createdb.py empty in order to automatically create .meta and .data files, which are describe example table abc.
Important! If you want to save your insertion data, you must run command begin before all commands, and run command commit after all other insert commands. Otherwise, after reloading server, all uncommited data will be deleted.
Query example: show tables
Result: show all tables, which is available (is in the /tmp/simpledb)
Query example: describe table table1
Result: show structure of table1
Query example: select * from table1
Result: show all records in table1
Query example: insert into table1 values (15,hello,NOW)
Result: if table1 have scheme as is in example above, this query add new record into table1 with id = 15, name = hello and dt = current time
Query example: delete from abc where id < 10
Result: remove all records, which id is less then 10
So, you can open many telnets and concurrently run transactions.
You must begin transaction with begin, after that you should write all queries in current transaction (note: you don't see any results, before you commit transaction).
To compute transaction and commit it, write commit.
To test this mechanism, you can run ruby insert.rb. This script runs 200 transactions with insertions concurrently, so after some seconds, all insertions will be correctly applied.
To check, open telnet and run select transaction:
begin
select * from abc
commit