Tacid

Transactional ACID key-value store with optional binary attachments, based on promises (async/await compatible) and LMDB (via node-lmdb).

Tacid abstracts away the transaction-handling of the underlaying LMDB. All operations performed within an env.with(...) - i.e. store.put(), store.get(), store.remove(), store.filter() - are automatically and efficiently wrapped in a transaction. Handling of parallel read and write transactions across multiple stores is covered as well.

Minimalistic API: put(), get(), remove(), filter(), count() and drop() are the only database operations that must be mastered to build high performance data services. Batch-operations are chained by Promise.all([...]).

usage

const { environment } = require('tacid')
const env = environment({ maxDbs: 1, path: '~/path/to/data/dir' })

env.with('my-store', myStore => {
    // Return a promise (all store.ops return promises)
    return myStore.put(key, value, /* optional attachment */)
  })
  .then(/* handle results */)
  .catch(/* handle errors */)

// Environments can be closed
env.close()

The example above initialises a database environment and accesses the store 'my-store' within it. A put-operation is performed on the store. Next to keys with associated values, binary attachments (NodeJS Buffers) can be stored.

environment() ->

<config>: environment configuration object literal, with following properties:

• path: mandatory string representing the directory path.
• maxDbs: mandatory number representing the max count of stores inside this environment.
• maxSize: optional max size of the environment.

<Environment>: instance representing a configured environment:

Environment API

• .with(<name>, <callback>): retrieve a store by name. Run operations on it from inside <callback> (see example above and store API below), return a thenable to commit all transactions.
• .close(): close environment.

Storage API

.put(key, value, attachment) -> Promise.resolve(key)

Write data to the store:

• <key>: string key under which value is stored. Best used with ID generators like auid.
• <value>: object literal representing the data to be stored. Must be serializable via JSON.stringify(...).
• <attachment>: an optional NodeJS buffer instance, additional binary data to be stored (e.g. a media file).
• Returns a Promise that resolves with the key.

.get(key) -> Promise.resolve(value|{ value, attachment })

Get data from the store:

• <key>: string key under which value is stored.
• Returns a Promise that resolves with the value or an object literal containing 2 props value and attachment.

.remove(key) -> Promise.resolve(value|{value, attachment})

Delete data from the store.

• <key>: string key under which value is stored.
• Returns a Promise that resolves with the value or an object literal containing 2 props value and attachment.

.count() -> Promise.resolve(number)

Get the number of key-value-pairs in the store.

• Returns a Promise that resolves with the number.

.filter([config,] callback) -> Promise.resolve(results[])

Filter contents of the store.

[config]: optional config

• { values: true }, provide to include values (attachments) during filtering.
• fallback if omitted: { values: false }, which means that filtering is over keys only.

<callback> will be called with ctx (context) as last argument:

• <ctx>: object with properties .index and .stop.
  • .index: the current index
  • .stop: a boolean set to false, will stop the filter process if set to true.
• If config { values: true } is provided, the callback is invoked (key, value, ctx) => {...}
• If config { values: false } is provided or config is omitted, the callback is invoked (key, ctx) => {...}
• Return true or false to keep or remove an item from the results set.

The result will always contain the keys and the values, e.g. { key: <a-key>, value: <a-value>|{ value: <a-value>, attachment: <an-attachment> } }.

Filtering by values

Keep in mind that most relational DBs are using key-value-stores like LMDB as their backing-store. So this kind of filtering is several times faster than to be expected with traditional DB-solutions, and perfectly valid.

Optimisation

Key-value stores are the kind of database used underneath traditional SQL-DBs. Without the overhead of clumsy and hazardous (security-wise) SQL-interpreters, though. So if you design your application for a key-value-store (in contrast to designing it for an intermediate SQL representation or even worse, another abstraction layer on top: ORM), it is very unlikely you'll encounter bad performance. That said please keep in mind:

• design your ERM for key-value-usage, not for an ORM
• you can include identification-attributes into the key, e.g. compose keys like: <primary-identification-attributes[:secondary-identification-attributes]>
• use an index per store, accessible with a fixed key
• store your data column-based if everything needs to be searchable

.drop()

Remove all entries from the store. <confirm-callback> is mandatory. Return true from the confirm callback to actually perform the drop of all entries.

.close()

Closes the store. The store composit cannot be used after calling close. A new store composit must be created via env.with(...).