* show picture insert / delete / update
* show indexes
* explain xids
* vacuum passes through heap
* vacuum passes through indexes
* visibility map
* [ freeze map ]
* manual vacuum
* autovacuum
  * triggers
    - autovacuum_vacuum_scale_factor
    - autovacuum_analyze_scale_factor
    - autovacuum_vacuum_threshold
    - autovacuum_analyze_threshold
    - autovacuum_freeze_max_age
  * rate limiting
    - vacuum_cost_page_hit = 1
    - vacuum_cost_page_miss = 10
    - vacuum_cost_page_dirty = 20
    - vacuum_cost_limit = 200
    - vacuum_cost_delay = 0
    - autovacuum_vacuum_cost_delay = 20
    - autovacuum_vacuum_cost_limit = -1 / vacuum_cost_delay
  - other tuning
    - vacuum_freeze_table_age
    - autovacuum_max_workers
    - autovacuum_naptime
  * tuning:
    - big enough maintenance_work_mem / autovacuum_work_mem
    - disable / tune cost limiting
    - WAL / IO tuning
      - max_wal_size (checkpoint_segments)
      - shared_buffers
    - prefetching relation before vacuum
* HOT
* issues
  * longlived transactions / snapshots
    - including (auto-)analyze!
    - snapshots are held till
  * no triggers on insert
    - index only scans!
  * wraparound scans extremely expensive
    - freeze map improves this in 9.6
* future improvements
  - freeze map (9.6)
  - parallel vacuum (10?)
  - "early tuple cleanup" (discussed, not fully started)
  - partial HOT tuples (some indexes updated)