Transactions

[aral]

A transaction is a series of updates on a table that are either all persisted together or are not persisted at all. They enable a table to have atomicity.

In JSDB, we write out our tables in JavaScript Data Format (JSDF), which is a transaction log in pure JavaScript. (Transaction log, in this case – confusingly – refers to a single update, not an atomic batch update).

To implement transactions (atomicity for batch changes) in JSDF, we can wrap multiple changes into a single-line immediately-invoked function expression (IIFE) and add that to our append-only log.

e.g.,

// ↑ other statements
(function () { _[0].name = 'Aral'; _[0].age = 43; })()

Without a transaction, the changes would be written out like this instead:

// ↑ other statements
_[0].name = 'Aral';
_[0].age = 43;

In keeping with as transparent an API as possible, here is one way we can implement this functionality:

db.people[0].__transaction-1__.name = 'Aral'
db.people[0].__transaction-1__.age = 43
await db.people.__transaction-1__.persist()

console.log('Transaction persisted.')

At this point we can be reasonably certain that transaction-1 has persisted to disk.

Note 1: transaction-1 is an arbitrary name, you can use any string that’s a valid identifier but it must start and end with two underscores and you must use the same identifier for any change that you want to include in your transaction.

Note 2: atomic transactions will only be implemented at the table-level (not the database-level, which would be a far messier undertaking and can be avoided by designing your tables accordingly).

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Mirrors internal issue: #1