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GeneralConcurrency options: Optimistic/Pessimistic/Last-Win Pin
devvvy26-Sep-03 7:59
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GeneralRe: Concurrency options: Optimistic/Pessimistic/Last-Win Pin
Marc Clifton27-Sep-03 3:39
mvaMarc Clifton27-Sep-03 3:39 
If I understand the three correctly:

Pessimistic concurrency control - a row is unavailable to users from the time the record is fetched until it is updated in the database.

Doesn't this mean that there's an assumption that the record is being fetched so that it can be updated? That would imply that during the time the client is hanging on to the record, nothing else can get done? Or is this referring only to the "fetch-change-put" time of the server, say, when an UPDATE command is executed? And isn't this method not really very usable in situations where the records are fetched and the connection closed? These assumptions would seem to be correct based on what the site says.

It's funny they use inventory as an example. I've written an inventory management system that uses optimistic concurrency. The connection is always open, and the only time there's violation is when someone is updating a record that is simultaneously being accessed. This hardly ever happens. 90% or more of the transactions are fetches--part look up, reporting, price lookup, qty look up, etc. Only when a part is received or sold is there a write transaction.

It would be impossible for me to run this system in a pessimistic mode, because records are always being fetched on a continuously open connection. And they're being fetched simply for read, not update, purposes.

Does that help, or am I misunderstanding something?

Marc



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GeneralRe: Concurrency options: Optimistic/Pessimistic/Last-Win Pin
Saikat Sen27-Sep-03 12:28
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GeneralRe: Concurrency options: Optimistic/Pessimistic/Last-Win Pin
devvvy29-Sep-03 7:59
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GeneralClient-Server Pin
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