Block based replication is the replication mechanism postgres incorporates natively. It's, in brief, sending all the
file-levelchanges to all the slaves, so the data folder is always the same. It's like having a replicated folder, not
includinglogs and some other things.
The disadvantage of block level replication, according to BDR, it that, when you have an open transaction, all DML is
writtento disk, even when the transaction is not committed. In a large transaction, all the date would be send to the
slaves,even when, at the end, the transaction is rolled back. With BDR, the transaction is sent to the other masters
onlyonce it's committed.
Of course, this can be a problem in both cases, depending on your environment. With block level replication, you can
getunnecessary traffic for transactions that would be finally rolled back(in contrast with BDR, which will send the
wholetransaction once it's committed); on BDR, you will get traffic peaks for some large transactions, as the whole
transactionis sent once it's committed(in contrast to block level replication, which would send changes as they are
beingexecuted). The later can also cause some delay, depending on the connection between the servers:
Regards,
Alvaro Aguayo
Jefe de Operaciones
Open Comb Systems E.I.R.L.
Oficina: (+51-1) 3377813 | RPM: #034252 / (+51) 995540103 | RPC: (+51) 954183248
Website: www.ocs.pe
----- Original Message -----
From: "Rakesh Kumar" <rakeshkumar464a3@gmail.com>
Cc: "PostgreSql-general" <pgsql-general@postgresql.org>
Sent: Monday, 13 June, 2016 07:13:09
Subject: Re: [GENERAL] BDR
http://bdr-project.org/docs/next/logical-vs-physical.html
"It (BDR) has significant advantages - and some disadvantages - when
compared to PostgreSQL's older physical (block-based) streaming or
archive-based replication with warm or hot standby"
What exactly is block based? Changes are recorded in the redo log,
right? Does that mean that in streaming replication, from redo log the
server applies changes at the block level of the data-file. That would
also mean that at any time, both primary and standby would be exactly
same, block by block.
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