The correct answers are A, C, and E.

buffers_backend shows the number of dirty buffers written by backend processes in order to allocate new buffers.

Each option is explained below.

A. It is displayed in the pg_stat_bgwriter view.
Correct.
The pg_stat_bgwriter view displays cluster-wide statistics related to the background writer process.

The following is an example of the output from the pg_stat_bgwriter view.
As shown in the example, it displays metrics such as buffers_backend and buffers_clean.

designet=# select * from pg_stat_bgwriter;
-[ RECORD 1 ]-----------------+------------------------------
checkpoints_timed | 72
checkpoints_req | 1
checkpoint_write_time | 185667
checkpoint_sync_time | 144
buffers_checkpoint | 2040
checkpoint_sync_time | 144 buffers_checkpoint | 2040
maxwritten_clean | 0
buffers_backend | 5563
buffers_backend_fsync | 0
buffers_alloc | 6590
stats_reset | 2019-02-03 14:34:39.343554+09
---- cut here ----

B. The value increases during write operations caused by checkpoints.
Incorrect.
It is the value of buffers_checkpoint that is increased when exporting by checkpoint.


C. If the value of buffers_backend is large compared to buffers_alloc, you should consider tuning the value of shared_buffers.
Correct.
buffers_alloc is the number of buffers allocated and shared_buffers is the amount of memory used by the database server for shared memory buffers.
The value of buffers_backend is increased by the backend process writing when it tries to allocate a new buffer and there is no room.
Therefore, if the value of buffers_backend is large relative to buffers_alloc, it is possible that the value of shared_buffers is insufficient. Therefore, tuning of the value of shared_buffres should be considered.

D. The value increases during write operations by the background writer.
Incorrect.
The buffers_clean value increases during write operations by the background writer.

E. The value increases during write operations by backend processes.
Correct.
When a backend process attempts to allocate a new buffer and finds no available space, it will write out a dirty buffer. This increases the buffers_backend value.