Thread: AW: [HACKERS] Optimizer fails?

AW: [HACKERS] Optimizer fails?

From
Zeugswetter Andreas SARZ
Date:
    There is one comment I would like to state, on the issue of
    a sequential scan beeing faster than an index scan. It is actually
often
    true in a singel user system that an index scan is more expensive
    than a sequential scan.
    As long as we have table level locks this is also true for heavyly
    concurrent access.
    Here comes the disadvantage:
    Once row or page locks will be implemented, the sequential scan
    cost should be reconsidered, since then readers will often be
waiting
    for updaters, that are actually updating data, that is irrelevant
for the
    reader. The average wait time will have to be added to the sequ.
scan
    cost.

    Andreas