Hi Srinivas, Multi-master replication in Postgres-R is handled using a process called certification that ensures there are no serializability violations. Look at the paper by Kemme and Alonzo entitled "Don't be Lazy, Be Consistent..." (http://www.cs.mcgill.ca/~kemme/papers/vldb00.html). In the first case you describe one transaction must abort if applying them would break serializability.
In the second case you describe, you must transmit read sets as well as write sets. The same sort of algorithm is applied as for writes. Please email me directly if you want more information. Thanks, Robert On 9/3/08 4:02 PM, "M2Y" <[EMAIL PROTECTED]> wrote: Hello, My basic question is: in multimaster replication, if each site goes ahead and does the modifications issued by the transaction and then sends the writeset to others in the group, how the ACID properties be maintained? Details: Suppose there are two sites in the group, lets say, A and B and are managing a database D. Two transactions TA and TB started in sites A and B respectively, at nearly same time, wanted to update same row of a table in the database. As, no locking structures and other concurrency handling structures are replicated each will go ahead and do the modifications in their corresponding databases and sends the writeset. Since, both writesets contain update to the same row, will the two transactions be rolled back or anything other than this happens? A more general question is: for Transactional isolation level 4(serializable level), the information such as locking of rows be transmitted across sites? If not, what is the mechanism to address concurrency with serializibility. Thanks, Srinivas -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers -- Robert Hodges, CTO, Continuent, Inc. Email: [EMAIL PROTECTED] Mobile: +1-510-501-3728 Skype: hodgesrm
