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Disk and Memory Characteristics

Conclusions

2) Cache disk pages in memory

Read a page:

• If present in the disk buffer, use it.

• If not, read from disk and add to buffer.

• If no unused frames in buffer, evict a page.
  • A clean page if possible.
  • A dirty page otherwise, (have to write it back to disk).

Issues:

• Which clean page (or dirty page) to evict?

• Doesn't this mean that uncommitted changes on dirty pages can be seen by other transactions?

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