sql server和oracle server之间的data migration：
site 1 用的是microsoft sql server， site 用的而是oracle server，
如果让用户能同时使用两个站点的DB，有下面几种方法，
请问各有哪些优缺点？
1、把S1的account复制到S2，再把S2的account复制到S1，再管理重复的account和进行ongoing account management。
2、Replicate DB1 at Site 2 (log shipping)
3、Replicate DB2 at Site 1 (log shipping)
4、Replicate DB1 at Site 2 (mirror)
5、Replicate DB2 at Site 1 (mirror)
6、Publish DB1, set Distributor, set DB2 as subscriber.
Publish DB2, set Distributor, set DB1 as subscriber
Each site holds DB1 and DB2 data (or subsets of data)
7、Migrate DB2 to SQL, then host DB2 at Site 1 (no DB in Site 2)
8、Create a link account for each DB, then establish database links in both directions:
Site 1 only holds DB1 data, Site 2 only holds DB2 data