From: Alvaro Herrera <alvhe...@2ndquadrant.com>
> So, we can know whether server is primary/standby by checking
> in_recovery, as opposed to knowing whether read-write which is done by
> checking transaction_read_only. So we can keep read-write as a synonym
> for "primary", and check in_recovery when used in servers that support
> the new GUC, and check transaction_read_only in older servers.
>
> It seems there's a lot of code that we can discard from the patch:
> first, we can discard checking for "read-only" altogether. Second, have
> us check transaction_read_only *only* if the server is of an older
> version.
Let me check my understanding. Are you proposing these?
* The canonical libpq connection parameter is target_session_attr = {primary |
standby | prefer-standby}. Leave and document read-write as a synonym for
primary.
* When the server version is 13 or later, libpq just checks in_recovery, not
checking transaction_read_only or sending SHOW transaction_read_only.
* When the server version is before 13, libpq sends SHOW transaction_read_only
as before.
Personally, 100% agreed, considering what we really wanted to do when
target_session_attr was introduced is to tell if the server is primary or
standby. The questions are:
Q1: Should we continue to use the name target_session_attr, or rename it to
target_server_type and make target_session_attr a synonym for it? I'm in favor
of the latter.
Q2: Can we accept the subtle incompatibility that
target_session_attr=read-write and target_server_type=primary are not the same,
when default_transaction_read_only is on? (I'd like to hear yes)
Q3: Can we go without supporting standby and prefer-standby for older servers?
(I think yes because we can say that it's a new feature effective for new
servers.)
Regards
Takayuki Tsunakawa
