-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi,
Le 14 déc. 08 à 16:48, Simon Riggs a écrit :
I am truly lost to understand why the *name* "synchronous replication" causes so much discussion, yet nobody has discussed what they would actually like the software to *do* (this being a software discussion list...). AFAICS we can make the software behave like *any* of the definitions discussed so far.
It seems that the easy parts are the one the more people will participate into. Maybe that's that simple.
We can make the reply to a commit message when any of the following events have occurred 1. We sent the message to standby 2. We received the message on standby 3. We wrote the WAL to the WAL file 4. We fsync'd the WAL file 5. We CRC checked the WAL commit record 6. We applied the WAL commit record
Ok, so let's talk about this easy part: my understanding of "synchronous replication" is that it gives to its users the strong guarantee that at commit time the transaction is secured to the slave(s). That means you get the D of ACID on more than one server.
Why synchronous? Because you know the durability is ensured exactly when you receive the COMMIT ack.
So I'm with Simon on this, the term Synchronous Replication does describe accurately what's being implemented here, and on the other hand, as so many of us are saying, it's true that it tells very little about it. Those 6 options are all in the scope of the infamous naming, just different guarantees level, from almost strong to very strong, with some "almost, but not quite, entirely unlike the strong I want". Pick your naming here too.
At least, that's how I'm understanding this, the bottom line of why care sending this email is that maybe it'll help some people to recover from sleep deprivation ;)
My 2¢, - -- dim -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (Darwin) iEYEARECAAYFAklFcEsACgkQlBXRlnbh1bk0YwCfa+zGBKTK5EoH/Nmu0x+R6vKI buAAniyL6Z+3MdT4rim5/xZQvdr4QOIQ =iHnY -----END PGP SIGNATURE----- -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
