Re: Streaming replication and unfit messages

Fujii Masao wrote:
> Hi,
> 
> When the replication connection is closed unexpectedly, walsender might emit
> the following unfit messages. IOW, the loss of the connection might be wrongly
> regarded as an arrival of invalid message by the walsender. This looks messy.
> We should get rid of that unfit FATAL message, emit a COMMERROR message and
> just call proc_exit() when the loss of the connection is found?
> 
>> [2460]: LOG:  could not receive data from client: No connection could be made because the target machine actively refused it.
>> [2460]: FATAL:  invalid standby closing message type 4
>> [2460]: LOG:  could not send data to client: No connection could be made because the target machine actively refused it.
> 
> Also the walsender wrongly tries to send the FATAL message to the standby even
> though the connection has already been closed, and then gets the following LOG
> message after the FATAL one. This FATAL message is suitable, but output of the
> LOG message looks messy, too. We should use COMMERROR instead of FATAL and then
> just call proc_exit() in order to prevent a message from being sent?
> 
>> [12586] FATAL:  unexpected EOF on standby connection
>> [12586] LOG:  could not send data to client: Broken pipe
> 
> The attached patch fixes those unfit messages.

Actually the pg_getbyte_if_available() function is a bit confused. The
comment above it claims that it returns 0 if no data is available
without blocking, but it actually returns -1 with errno==EWOULDBLOCK.
That stems from confusion in secure_read(); with SSL it returns 0 if it
would block, but without SSL it returns -1 and EWOULDBLOCK. We should
fix that so that secure_read() behaves consistently and so that
pq_getbyte_if_available() behaves like e.g pq_getbytes().

Patch attached for that. pq_getbyte_if_available() now reports any
errors with COMMERROR level, and returns EOF if the connection is closed
cleanly. If no data is available without blocking it now really returns
0 as the comment said. Walsender reports any unexpected EOF to the log
at COMMERROR level, similar to what normal backends do.

-- 
  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com