Implement db#clear across the board

[vweevers]

Background: Level/abstract-leveldown#24 (comment).

Phase 1: get it working

• The default implementation of clear() deletes entries with an iterator. It can take range options, e.g. clear({ gt: 'foo' }) and should serialize them
  • PR: Level/abstract-leveldown#310
  • Release: 6.1.0
• encoding-down can call this.db.clear() and should encode the range options
  • PR: Level/encoding-down#89)
  • Release: 6.2.0
• leveldown
  • PR: Level/leveldown#660
  • Release: 5.2.0
• deferred-leveldown should defer it
  • PR: Level/deferred-leveldown#72
  • Release: 5.2.0
• levelup
  • PR: Level/levelup#669
  • Release: 4.2.0
• memdown
  • PR: Level/memdown#194
  • Release: 5.0.0
• level-packager (bump dependencies to prevent dedupe)
  • Commit: Level/packager@a293d30
  • Release: 5.0.3
• level-js
  • PR: Level/level-js#182
  • Release: 5.0.0
• level
  • PR or commit: Level/level#162, Level/level@5efdc82
  • Release: 6.0.0
• level-mem (bump dependencies to prevent dedupe)
  • Commit: Level/mem@baec173
  • Release: 5.0.1
• rocksdb
  • Commit: Level/rocksdb@b9d58fb
  • Release: 4.1.0
• level-rocksdb (bump dependencies to prevent dedupe)
• subleveldown uses the range options to implement clear on a sublevel
  • PR: Level/subleveldown#74
  • Release: 4.1.2
• multileveldown (and by extension, level-party)
  • Level/multileveldown@47e0137
  • Release: 5.0.0
• leveldown-hyper and level-hyper (slated to be deprecated)

Phase 2: optimize

• memdown: Level/memdown#213
• leveldown can implement it natively (Level/leveldown#680)
• rocksdb: Level/rocksdb#184 (5.2.0)
• level-js can call either IDBObjectStore#clear() or IDBObjectStore#delete(range)

On the side

• Use it in mafintosh/level-temp (old)
• Add notice to Raynos/level-delete-range (old)
• juliangruber/level-delete-stream#3
• Send PR to noffle/kappa-view-level for its clearIndex()

[ralphtheninja]

Very nice. I especially like the subleveldown feature, like emptying a bucket of stuff.

[vweevers]

Relevant leveldown issue: Level/leveldown#9.

[vweevers]

Ah, the level-concat-iterator dependency comes in handy for the default implementation of _clear :)

[ralphtheninja]

Ah, the level-concat-iterator dependency comes in handy for the default implementation of _clear :)

Good. Then we don't have to feel so bad about including it 😉

[vweevers]

Ah, the level-concat-iterator dependency comes in handy for the default implementation of _clear :)

Scratch that. Would choke on many keys.

[vweevers]

Because abstract-leveldown@6.1.0 now has a clear() method, I'm moving this issue to community to track overall progress.