> okay, so it seems we need few things which middleware (Pangea) expects > if we have to follow the design of paper.
Yes. > I haven't read the paper completely but it sounds quite restrictive > (like both commits and snapshots need to wait). Maybe. There is a performance evaluation in the paper. You might want to take a look at it. > Another point is that > do we want some middleware involved in the solution? The main thing > I was looking into at this stage is do we think that the current > implementation proposed by the patch for 2PC is generic enough that we > would be later able to integrate the solution for atomic visibility? My concern is, FDW+2PC without atomic visibility could lead to data inconsistency among servers in some cases. If my understanding is correct, FDW+2PC (without atomic visibility) cannot prevent data inconsistency in the case below. Initially table t1 has only one row with i = 0 on both N1 and N2. By executing S1 and S2 concurrently, t1 now has different value of i, 0 and 1. S1/N1: DROP TABLE t1; DROP TABLE S1/N1: CREATE TABLE t1(i int); CREATE TABLE S1/N1: INSERT INTO t1 VALUES(0); INSERT 0 1 S1/N2: DROP TABLE t1; DROP TABLE S1/N2: CREATE TABLE t1(i int); CREATE TABLE S1/N2: INSERT INTO t1 VALUES(0); INSERT 0 1 S1/N1: BEGIN; BEGIN S1/N2: BEGIN; BEGIN S1/N1: UPDATE t1 SET i = i + 1; -- i = 1 UPDATE 1 S1/N2: UPDATE t1 SET i = i + 1; -- i = 1 UPDATE 1 S1/N1: PREPARE TRANSACTION 's1n1'; PREPARE TRANSACTION S1/N1: COMMIT PREPARED 's1n1'; COMMIT PREPARED S2/N1: BEGIN; BEGIN S2/N2: BEGIN; BEGIN S2/N2: DELETE FROM t1 WHERE i = 1; DELETE 0 S2/N1: DELETE FROM t1 WHERE i = 1; DELETE 1 S1/N2: PREPARE TRANSACTION 's1n2'; PREPARE TRANSACTION S2/N1: PREPARE TRANSACTION 's2n1'; PREPARE TRANSACTION S2/N2: PREPARE TRANSACTION 's2n2'; PREPARE TRANSACTION S1/N2: COMMIT PREPARED 's1n2'; COMMIT PREPARED S2/N1: COMMIT PREPARED 's2n1'; COMMIT PREPARED S2/N2: COMMIT PREPARED 's2n2'; COMMIT PREPARED S2/N1: SELECT * FROM t1; i --- (0 rows) S2/N2: SELECT * FROM t1; i --- 1 (1 row) Best regards, -- Tatsuo Ishii SRA OSS, Inc. Japan English: http://www.sraoss.co.jp/index_en.php Japanese:http://www.sraoss.co.jp
