Gaetano Mendola <[EMAIL PROTECTED]> writes: > [ use list with master node and circular linking ]
> now is very late here ( 04:17 AM ) so I wrote > the wrong code ( not checked ) but show the idea of > avoid "if". This saves an "if" during addition of a list item, at the cost of greater expense during list traversal. (Instead of a loop termination test like "ptr != NULL", you need something like "ptr != master_node". This may not take an extra cycle, but only if you can afford to dedicate a register to holding the value of master_node within the loop. That hurts, especially on architectures with not very many registers.) Offhand I do not see a win here. Node addition implies a palloc which means you are going to be jumping control all over the place anyway; there's no way that eliminating one "if" in that path of control is going to be a meaningful improvement. Saving a cycle or two during list traversal could be a meaningful improvement, though. By the same token, keeping a length count in the master node might be a waste of cycles, but it's going to be a pretty tiny waste compared to the other overhead of adding or removing a node. The potential savings from making length() be a constant-time operation seem like a win to me. Anyway, we should build the code that way and then do profiling with and without support for constant-cost length(). regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 7: don't forget to increase your free space map settings