Re: REUSEDLT and performance

At 09:07 AM 2/1/01 -0600, you wrote:
>Are there performance implications when using REUSEDLT, especially on 
>really large files? I have to think that there is at least some 
>performance hit when REUSEDLT is enabled for files with millions of 
>records. I'd guess that the system keeps some sort of index of deleted 
>records, and serves one of those up when a WRITE is issued. I suppose, 
>done correctly, the performance implications aren't too great; it would 
>only affect deletes (add an entry to the index) and writes (fetch the 
>record number from the index rather than just use the next sequential record).
>
>Has anybody looked at this in any detail?


I have done a lot of detailed work here.  The only (significant) 
performance implications when using this feature occur if you are 
constantly adding/deleting records over the limit of the maximum number of 
records in the file, which (IMHO) is not typical.

When the system does, is it creates a "deleted records map" (of RRN) at 
file open time, and uses this as a directory of where to add records.  Once 
a file has opened, a subsequently deleted record will not be known to the 
job that already has the file open.

Al




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