Re: A thought on Index Organized Tables
| От | Gokulakannan Somasundaram |
|---|---|
| Тема | Re: A thought on Index Organized Tables |
| Дата | |
| Msg-id | 9362e74e1002242319w18d0524di21fd13ba5dabfc4f@mail.gmail.com обсуждение |
| Ответ на | Re: A thought on Index Organized Tables (Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>) |
| Ответы |
Re: A thought on Index Organized Tables
|
| Список | pgsql-hackers |
The WAL record of the heap insert/update/delete contains a flag
indicating that the visibility map needs to be updated too. Thus no need
for a separate WAL record.
Heikki,
Have you considered these cases?
a) The current WAL architecture makes sure that the WAL Log is written before the actual page flush( i believe ). But you are changing that architecture for Visibility maps. Visibility map might get flushed out before the corresponding WAL gets written. I think you would then suggest full page writes here
b) Say for a large table, you have multiple buffers of visibility map, then there is a chance that one buffer gets flushed to the disk and the other doesn't. If the WAL records are not in place, then this leads to a time inconsistent visibility map.
c) If you are going to track all the WAL linked with a buffer of visibility map, then you need to introduce another synchronization in the critical path.
May be i am missing something? I am asking these questions only out of curiosity.
Thanks,
Gokul.
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