> Does sync replication guarantee that any inserted data on primary is
> immediately visible for read on standbys with no lag.
Basically yes. Of course there is *some* latency, at the very least
from the network.
If I run a process on a standby machine that displays a value every
0.1 sec and update the value on the master, I see the standby updating
with a lag that feels less than 0.2 sec or so.
You might have lag, however, in situations where you have so much
write into the master that the network or standby is not able to
catch up. After the write burst is over, the stanby will catch up
as it quickly as possible, though.
Also, you use the word "consistency", that would be something else...
Of course you always get consistent data, lag or not. This is Postgres
after all :)
Bye,
Chris.