README
Baby DB
A easy-to-use, robust, file-based DB for Node. Acts as an append-only store for objects.
Motivation
When writing NodeJs projects I often find I need an easy-to-use, understandable, yet robust database that I can throw into my project without needing to install another database server and configure a connection etc.
What I needed was a dead simple library that I could plug into any project and that would:
- Keep data persisted safely
- Be easy to examine & understand
- Be easy to backup
- Be able to scale up reasonably well for small to mid-sized projects.
And so Baby DB was born.
How to Use Baby DB
Baby DB stores data in an append only log file. This makes it almost impossible to lose data (except if the underlying hardware fails). It’s also a very flexible way to store data - it’s easy to add fields, change the schema and so on by upgrading the processor.
Each instance requires us to pass in a “processor” that consumes each record and aggregates or stores it for use by the rest of the system. Baby DB itself streams the data records so it has very low memory overhead.
To keep things simple, while you could have all data stored in a single log file, it may be better to store each “table” of data in it’s own file.
Example
const babydb = require('baby-db')
...
const userdb = babydb(userfile)
userdb.on('error', err => console.error(err))
userdb.on('rec', (rec, linenum) => {
switch(rec.type) {
case 'new':
USERS[rec.userid] = rec.info
break
case 'update':
if(!USERS[rec.userid]) throw `Cannot update non-existent record on line: ${linenum}`
Object.assign(USERS[rec.userid], rec.info)
break
case 'delete':
delete USERS[rec.userid]
break
default:
throw `Did not understand record type: "${rec.type}", on line: ${linenum}`
}
})
userdb.on('done', () => {
const jack = 2;
userdb.add({ type: 'new', userid: jack, info: { name: 'jack', mood: 'annoyed'}})
userdb.add({ type: 'update', userid: jack, info: { mood: 'really annoyed'}})
userdb.add({ type: 'delete', userid: jack})
const jill = 3;
userdb.add({ type: 'new', userid: jill, info: { name: 'jill', mood: 'sleepy'}})
userdb.add({ type: 'update', userid: jill, info: { mood: 'hungry'}})
console.log("ready to rumble....!")
})
babydb.onExitSignal(() => process.exit())
Clean Exits
Baby DB is designed to support persisting it’s data and cleanly exiting. You can do this by calling db.stop()
or (recommended), by installing the onExitSignal()
handler which will trap all common exit signals and flush the data to disk.
babydb.onExitSignal(() => {
process.exit() // use process.exit() otherwise the application will not exit
})
Options
Baby DB supports the following options (defaults shown):
const userdb = babydb(file, {
loadOnStart: true, // otherwise call load()
saveEvery: 3000, // persist to disk every 3 seconds
maxRecsEvery: 3072, // any additional spike of records beyond 3072 every 3 seconds will raise an 'overflow' event
unmanaged: false, // stopAll() and onExitSignal() will ignore this database if true
rolloverLimit: 0 // causes the file to roll over when the number of records goes over (see below)
})
Rollover
When using an append-only log, it's common to find that it grows very large very quickly.
Baby DB handles this problem by allowing you to specify a rolloverLimit
in your options. Once the number of records in a file goes beyond this number, it is archived in the format:
filename-<timestamp>-<number of records>.ext
NB: The number of records in the file could be above the actual rolloverLimit
depending on how many additional records came in during the write period.
Snapshot record(s)
When we set a rollover, the old records are no longer processed and so, if they need to be, it is helpful to add some 'summary' records at the start of the new roll(-ed)-over file that captures what we need from the old records. To do this, listen for the 'rollover' event and use that to add the summary records. For example:
babydb.on('rollover', () => babydb.add({ type: 'summary', info: { ... }, meta: { ... }}))
Overflow
Baby DB provides an option for ignoring data ‘spikes’ that may come up either accidentally or due to some malicious intent.
To handle overflow records, listen for the ‘overflow’ event:
userdb.on('overflow', rec => {
// alert the navy
save_somewhere_else(rec)
})
By default more than 1024 records every second is considered an ‘overflow’. This is easily changed using the options described in the Options section. In particular, setting the maxRecsEvery
parameter to 0
will have BabyDB never mark any records as ‘overflow’.
Enjoy!