Level TTL

Add a 'ttl' (time-to-live) option to LevelUP for put() and batch()

Augment LevelUP to handle a new 'ttl' option on put() and batch() that specifies the number of milliseconds an entry should remain in the data store. After the TTL, the entry will be automatically cleared for you.

Requires LevelUP (or Level) to be installed separately.

Note: version 1.0.0 data stores are not backward compatible with previous versions. If you have unexpired entries in a data store managed by pre-1.0.0, don't expect them to expire if you upgrade to 1.0.0+. This is due to a level-sublevel change. It is also recommended that you only use level-sublevel 6.0.0+ with level-ttl.

var levelup  = require('level')
  , ttl      = require('level-ttl')

var db = levelu('/tmp/foo.db')
db = ttl(db)

// --------------------------- put() --------------------------- //
// this entry will only stay in the data store for 1 hour
db.put('foo', 'bar', { ttl: 1000 * 60 * 60 }, function (err) { /* .. */ })

// -------------------------- batch() -------------------------- //
// the two 'put' entries will only stay in the data store for 1 hour
db.batch([
    { type: 'put', key: 'foo', value: 'bar' }
  , { type: 'put', key: 'bam', value: 'boom' }
  , { type: 'del', key: 'w00t' }
], { ttl: 1000 * 60 * 60 }, function (err) { /* .. */ })

If you put the same entry twice, you refresh the TTL to the last put operation. In this way you can build utilities like session managers for your web application where the user's session is refreshed with each visit but expires after a set period of time since their last visit.

Alternatively, for a lower write-footprint you can use the ttl() method that is added to your LevelUP instance which can serve to insert or update a ttl for any given key in the database (even if that key doesn't exist but may in the future! Crazy!).

db.put('foo', 'bar', function (err) { /* .. */ })
db.ttl('foo', 1000 * 60 * 60, function (err) { /* .. */ })

Level TTL uses an internal scan every 10 seconds by default, this limits the available resolution of your TTL values, possibly delaying a delete for up to 10 seconds. The resolution can be tuned by passing the 'checkFrequency' option to the ttl() initialiser.

var db = level('/tmp/foo.db')
// scan for deletables every second
db = ttl(db, { checkFrequency: 1000 })

/* .. */

Of course, a scan takes some resources, particularly on a data store that makes heavy use of TTLs. If you don't require high accuracy for actual deletions then you can increase the 'checkFrequency'. Note though that a scan only involves invoking a LevelUP ReadStream that returns only the entries due to expire, so it doesn't have to manually check through all entries with a TTL. As usual, it's best to not do too much tuning until you have you have something worth tuning!

Shutting down

Level TTL uses a timer to regularly check for expiring entries (don't worry, the whole data store isn't scanned, it's very efficient!). The db.close() method is automatically wired to stop the timer but there is also a more explicit db.stop() method that will stop the timer and not pass on to a close() underlying LevelUP instance.

Contributors

Level TTL is powered by the following hackers:

dey-dey / node-level-ttl

Level TTL

Shutting down

Contributors

Licence

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