Обсуждение: DRDB?
Hi all, is DRDB (http://www.drbd.org/) a recommended replication-solution for PostgreSQL? I asked some PostgreSQL-People and DRDB-People on the Linux-Tag in germany. But I'm not very assured about this solution. Which is the best solution? (Slony, DRDB, WAL or something else?) Best regards, Martin
Martin Fandel wrote: > Hi all, > > is DRDB (http://www.drbd.org/) a recommended replication-solution for > PostgreSQL? I asked some PostgreSQL-People and DRDB-People on the > Linux-Tag in germany. But I'm not very assured about this solution. Uh, we really don't _recommend_ replication solutions. However, I will say I have heard of Slony, but never of DRDB. It seems DRDB replicates the file system blocks to another machine. While this could work just fine, it is different than something like Slony that allows you to replicate only certain tables and allows for you to switch master and slave roles among servers. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
Bruce Momjian <pgman@candle.pha.pa.us> writes: > Martin Fandel wrote: >> is DRDB (http://www.drbd.org/) a recommended replication-solution for >> PostgreSQL? I asked some PostgreSQL-People and DRDB-People on the >> Linux-Tag in germany. But I'm not very assured about this solution. > Uh, we really don't _recommend_ replication solutions. However, I will > say I have heard of Slony, but never of DRDB. It seems DRDB replicates > the file system blocks to another machine. I have not probed further than the site's top page, but unless DRBD offers some pretty strong guarantees about physical write order on the master being duplicated on the slave, it won't work reliably for Postgres. regards, tom lane
> Bruce Momjian <pgman@candle.pha.pa.us> writes: > > Martin Fandel wrote: > >> is DRDB (http://www.drbd.org/) a recommended > replication-solution for > >> PostgreSQL? I asked some PostgreSQL-People and DRDB-People on the > >> Linux-Tag in germany. But I'm not very assured about this solution. > > > Uh, we really don't _recommend_ replication solutions. However, I > > will say I have heard of Slony, but never of DRDB. It seems DRDB > > replicates the file system blocks to another machine. (Um, Bruce, we talked to Alan Robertson about this in Copenhagen a couple of months back. So you've certainly *heard* of it :P) > I have not probed further than the site's top page, but > unless DRBD offers some pretty strong guarantees about > physical write order on the master being duplicated on the > slave, it won't work reliably for Postgres. From what I've heard, it does guarantee this. I think it requires you to put all your stuff on the same DRBD device (no special device for WAL). But I'm not 100% sure on this. For example, DB2 is supported on these devices. I would assume they have the same requirements as postgresql in this case. (See ftp://ftp.software.ibm.com/software/data/pubs/papers/db2halinux.pdf) //Magnus
"Magnus Hagander" <mha@sollentuna.net> writes:
>> I have not probed further than the site's top page, but
>> unless DRBD offers some pretty strong guarantees about
>> physical write order on the master being duplicated on the
>> slave, it won't work reliably for Postgres.
> From what I've heard, it does guarantee this. I think it requires you to
> put all your stuff on the same DRBD device (no special device for WAL).
That would seem pretty likely --- I don't see how a block-level driver
could synchronize operations occuring on different devices.
regards, tom lane
Magnus Hagander wrote: > > Bruce Momjian <pgman@candle.pha.pa.us> writes: > > > Martin Fandel wrote: > > >> is DRDB (http://www.drbd.org/) a recommended > > replication-solution for > > >> PostgreSQL? I asked some PostgreSQL-People and DRDB-People on the > > >> Linux-Tag in germany. But I'm not very assured about this solution. > > > > > Uh, we really don't _recommend_ replication solutions. However, I > > > will say I have heard of Slony, but never of DRDB. It seems DRDB > > > replicates the file system blocks to another machine. > > (Um, Bruce, we talked to Alan Robertson about this in Copenhagen a > couple of months back. So you've certainly *heard* of it :P) Oh, that was it. Yea, I remember now! -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
Martin Fandel wrote: > Which is the best solution? (Slony, DRDB, WAL or something else?) Slony is a master/slave replication system that can improve overall read performance. DRBD gives you a hot stand-by system. Both of these are completely different goals, which can be implemented complementarily. A WAL-based replication gives you about the same effect as a DRBD replication, but with DRBD you pass on all the responsibility to the operating system. One guy at LinuxTag told be he manages his DRBD pairs using Linux virtual servers, which would mean that on some level you don't even notice that you have two machines running instead of one. If have yet to figure that out, but it sounds quite nice. Btw., it was probably me who told you about DRBD, but I didn't make that up myself. A lot of people are currently using it. -- Peter Eisentraut http://developer.postgresql.org/~petere/