On Mon, 20 Feb 2017 09:09:05 -0600, Tom Marchant wrote: > >>> Huge directory provides really >>> poor performance. >> >>Unless cached by LLA or another directory caching product. > >I'm not sure that helps much. > >The poor performance that Radoslaw mentioned is more on directory updates. >If you create a member (insert a directory entry), the last entry will >probably >be pushed off the end of the directory entry block. That entry will be moved >to the next block, and probably push the last entry off that block. This >process will continue to the end of the directory. > Is this equally true for PDSE as for PDS? Does a PDSE still have a directory organized in 256-byte blocks? Does SEARCH KEY HIGH OR EQUAL work alike on PDSE pages? (I know; it's NDA.)
BPAM supports UNIX directories, but read-only. Still, what's the format of the token used by NOTE and POINT for UNIX directory members? Record number would be dreadfully inefficient for RECFM=VB. How about for FILEDATA=RECORD? >Similarly, if a member is deleted, the space that remains at the end of the >block >will probably be big enough to hold the first entry on the next track. If it >is, that >entry will be moved, leaving room at the end of that block. Again, if the >first >entry on the block after that one will fit, and it probably will, it is also >moved. >Again, this process continues to the end of the directory. > >The directory is always maintained in member name order, and all of the >directory >blocks except the last one are always kept as full as possible. > >For directory searches, SEARCH KEY HIGH OR EQUAL is used, allowing the >correct block to be read with a minimum of CPU processing and data transfer. > >-- >Tom Marchant > >---------------------------------------------------------------------- >For IBM-MAIN subscribe / signoff / archive access instructions, >send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
