TokuMX Hot Indexing

Background

• Vanilla MongoDB supports background indexing. The client thread builds the index using regular indexed insertions and yields the DBWrite lock perodically. This makes the operation online.
• TokuDB for MySQL supports hot indexing which has a similar user experience to background indexing.
• TokuMX should be able to support background indexing by initiating the index build in a DBWrite lock and performing the actual build in a DBRead lock. Committing the hot index will take the DBWrite lock.

Design

• Break up index builds into three stages:
  • Write locked: Prep (validation, setup, mark the ns as containing a hot index)
  • Read locked: Build (build the index)
  • Write locked: Commit (finalize the index, mark the ns as not containing a hot index)
• Capture system.indexes inserts higher in the stack
  • Allows for the above locking scheme.
• Implementation notes:
  • _indexBuildInProgress is the hot index marker.
  • _indexes.size() is the number of total indexes
  • _nIndexes is the number of usable indexes
  • _indexes[_nIndexes] is the hot index, if in progress.
  • If a hot index aborts, the nsindex must rollback and close the affected ns.

Testing

• Initiating a hot index build:
  • Cannot already have a hot index in progress for the ns.
  • ...plus all the normal rules for creating an index.
• During a hot index build:
  • Inserts/updates/deletes should work.
  • Cannot dropIndexes/dropDatabase if a hot index is in progress.
  • Cannot run optimize on a hot index.
  • Cannot force the query optimizer to use a hot index.
  • Cannot update by _id if one of the fields is in a hot index key.
• After a hot index build:
  • Should be possible to drop the index.
  • Should be possible to query the index.