Read consistency depends on the active Transaction Isolation Level. Here, you trade off consistency requirements against performance and additional error states.
Most applications get away with rather "weak" isolation guarantees, because a JOIN would still not return inconsistent data. For example,
CREATE TABLE one (a INTEGER PRIMARY KEY, b INTEGER ...
I'll try to answer only 1:
When the data is distributed across multiple servers (ex 1 master- n slaves configuration)
Do relational databases ensure consistency in reads? I mean a committed read is immediately available to be read by other transactions? I suspect not given network is involved, making Relational DBs as eventual consistent DBs.
This depends ...
To directly answer your questions:
"Do relational databases ensure consistency in reads?"
A: In short, when the ACID principals, and specifically the Consistency part, were defined, this was long before distributed data was a concept for relational databases. So the Consistency from that standpoint was automatic because there's only a single ...