Jacek, I assume "time partitioning" = separating tables on disk by time attribute, e.g. one disk holds part of the table for "today", another for "tomorrow", an so on.
The goal of partitioning is to distribute the read operation over maximum number of independent disks, to speed up the retrieval (the disks are still bound to one CPU, otherwise this technically would be partitioning + federating). In time partitioned DB, the query that will benefit from this is something like: "give me the time history of a given object", i.e. essentially retrieving a light curve. It is safe to say there are use cases for work on light curves, so time partitioning should definitely be considered for source tables. To answer your question, I don't think either schema (uw or llnl) implies any partitioning yet -- you can partition any table by any of its attributes, including the time domain. Hope this helps, Sergei. > In article <[EMAIL PROTECTED]>, > Jacek Becla <[EMAIL PROTECTED]> wrote: > >> > - do either of the current prototype schemas (UW and sergei's) >> > have time partitioning in mind? >> Sergei, Nicole and Russ, can you answer this? > > What is time partitioning? > > The UW database has a TAI field for each image. Object link to images, so it's easy to find the time at which a given object was measured. > > If integration time varies across the image (as is likely for LSST if a shutter is used, as somebody pointed out at a recent phone con), then: - Additional information is needed in the object table to allow > computing time as a function of position on the image. > - The time of each source should probably be computed as sources are detected, and stored as a separate TAI field in the source table. > > We have run into this issue ourselves. Time varies across the image for SDSS data (drift-scanned data). Our Image table has TAI and RowTime such that TAI of source = TAI of image + RowTime*CtrY. However, we have not yet added a TAI field to our Object table. > > -- Russell > > _______________________________________________ > LSST-data mailing list > [email protected] > http://www.lsstmail.org/mailman/listinfo/lsst-data > _______________________________________________ LSST-data mailing list [email protected] http://www.lsstmail.org/mailman/listinfo/lsst-data
