At 01:51 25/05/01 +0500, Hannu Krosing wrote:
>
>How does it do MVCC with an overwriting storage manager ?
>
I don't know about Oracle, but Dec/RDB also does overwriting and MVCC. It
does this by taking a snapshot of pages that are participating in both RW
and RO transactions (De/RDB has the options on SET TRANSACTION that specify
if the TX will do updates or not). It has the disadvantage that the
snapshot will grow quite large for bulk loads. Typically they are about
10-20% of DB size. Pages are freed from the snapshot as active TXs finish.
Note that the snapshots are separate from the journalling (WAL) and
rollback files.
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