Append-only logs are a nifty way to share key-value data.
Unfortunately, append-only logs grow forever. Compacting can be
tricky, especially at the same time you're trying to share.
revlog stores delta-encoded key-value data in an append-only log.
Rather than replay entries from oldest to newest, clients rewind
entries from newest to oldest. As the log rewinds, it keeps track of
the keys for which it has seen values and drops superseded entries,
so every rewind compacts the log.
RevLog supports five abstract operations:
Set a key to a value on the log. Very quick.
Unset the value of a key on the log. Very quick.
Find the index number of the latest log entry. Very quick.
Stream key-value entries, with index numbers, in reverse.
A streaming operation, but builds a trie of key names in memory
to facilitate compaction in passing.
Read the value at a specific key, if any. Relatively slow.
API Examples
The following examples are also the package's test suite, using
Node.js' built-in assert module.
var assert =require('assert')
Initialization
revlog stores log data in a LevelUP. The LevelUP must be able
to encode string keys and nested Object values.
The examples in this file use a LevelUP with JSON-encoded values
backed by memdown, an in-memory storage back-end. You could
also use LevelDOWN, LevelUP's default, disk-persisted,
log-structured-merge-tree-based store.