On 12.04.2011 19:42, jagan wrote:
Where is the OID of tuple stored in a WAL record of a tuple? If not with xl_heap_header, where is it stored? Is it stored at all?> It's stored in the "tuple data" portion. Is the OID also recorded with xl_heap_delete record as well or just the xl_heaptid? From my reading of the code it is not recorded.
Correct, it's not.
In general, why is OID of a tuple relegated as just another tuple data, when it can replace xl_heaptid as a much more stable tuple identifier. I understand that by recording tuples in terms of xl_heaptid (i.e., page/offset) means that the db can recover quickly but isn't there some value to storing a much "higher level" information in the WAL logs? For example, tuple manipulations, if recorded in terms of manipulation on tuple oids, can support applications such as these: http://blogs.enterprisedb.com/2011/03/03/more-musings-on-logical-replication/
Possibly. On the other hand, another common complaint is that PostgreSQL writes a lot of WAL, much more than other DBMSs. Adding more higher-level information to WAL records would make that issue even worse. At the moment we only include the minimum amount of information needed for recovery.
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