rename pg_log_standby_snapshot

Hi,

While looking at [1] which introduces a new function called pg_log_query_plan to
write an explain plan to the log file, I noticed that we currently
have overloaded
the meaning of the "pg_log_" prefix.

Currently there is pg_log_backend_memory_contexts which logs memory
contexts to the log file, but there is also a pg_log_standby_snapshot which
takes a snapshot of running transactions and writes them to wal, so it has
nothing to do with writing to the log file.

List of functions
Schema | Name | Result data type |
Argument data types | Type
------------+--------------------------------+------------------+---------------------+------
pg_catalog | pg_log_backend_memory_contexts | boolean |
integer | func
pg_catalog | pg_log_standby_snapshot | pg_lsn |
| func
(3 rows)

Should the pg_log_ prefix strictly refer to functions that write to
logs? If so, should we rename
pg_log_standby_snapshot to something else, such as
pg_standby_snapshot_xip_to_wal?
This name is long, but it is still shorter than other system function
names and clearly describes
what the function does.

Additionally, this name is similar to pg_snapshot_xip, which returns
in-progress transactions.

Also, pg_snapshot_ is a good prefix for future functions that operate
on standbys only.

Another minor thing: the documentation for pg_log_standby_snapshot
function currently says,
"Take a snapshot of running transactions and write it to WAL."
However, we commonly refer to these transactions as "in-progress transactions."
So, maybe the documentation should say, "Take a snapshot of
in-progress transactions and write it to WAL."

[1] https://www.postgresql.org/message-id/flat/0e0e7ca08dff077a625c27a5e0c2ef0a%40oss.nttdata.com#6539312988e4695d2d416688a3ab34fa

--
Sami Imseih
Amazon Web Services (AWS)