Fix monitor view pg_stat_bgwriter & pg_stat_checkpoiner

Create system view pg_stat_checkpointer (Bharath Rupireddy, Anton A. Melnikov, Alexander Korotkov)

Relevant columns have been removed from pg_stat_bgwriter and added to this new system view.

The pg_stat_bgwriter view will always have a single row, containing data about the background writer of the cluster.

Table 27.24. pg_stat_bgwriter View

Column TypeDescription
`buffers_clean` `bigint`Number of buffers written by the background writer
`maxwritten_clean` `bigint`Number of times the background writer stopped a cleaning scan because it had written too many buffers
`buffers_alloc` `bigint`Number of buffers allocated
`stats_reset` `timestamp with time zone`Time at which these statistics were last reset

The pg_stat_checkpointer view will always have a single row, containing data about the checkpointer process of the cluster.

Table 27.25. pg_stat_checkpointer View

Column TypeDescription
`num_timed` `bigint`Number of scheduled checkpoints that have been performed
`num_requested` `bigint`Number of requested checkpoints that have been performed
`restartpoints_timed` `bigint`Number of scheduled restartpoints due to timeout or after a failed attempt to perform it
`restartpoints_req` `bigint`Number of requested restartpoints
`restartpoints_done` `bigint`Number of restartpoints that have been performed
`write_time` `double precision`Total amount of time that has been spent in the portion of processing checkpoints and restartpoints where files are written to disk, in milliseconds
`sync_time` `double precision`Total amount of time that has been spent in the portion of processing checkpoints and restartpoints where files are synchronized to disk, in milliseconds
`buffers_written` `bigint`Number of buffers written during checkpoints and restartpoints
`stats_reset` `timestamp with time zone`Time at which these statistics were last reset

Vonng / pigsty