Memory usage and ZEBRA

[HMEMOUSE]

The HBOOK system uses the ZEBRA data manager to store its data elements in a COMMON block /PAWC/ (shared with the KUIP and HIGZ packages, when the latter are also used, as is the case in PAW). In fact the first task of a HBOOK user is to declare the length of this common to ZEBRA by a call to HLIMIT, as is seen in figures [more info] and [more info]

In the /PAWC/ data store, the HBOOK, HIGZ and KUIP packages have all their own division (see [bib-ZEBRA] for more details on the notion of divisions) as follows (see figure [more info]):

LINKS

Some locations at the beginning of /PAWC/ for ZEBRA pointers.

WORKS

Working space (or division 1) used by the various packages storing information in /PAWC/

HBOOK

Division 2 of the store. Reserved to HBOOK

HIGZ

A division reserved for the HIGZ graphics package. This division only exists when HIGZ is called.

KUIP

A division reserved for the KUIP user interface package. This division only exists when KUIP is called.

SYSTEM

The ZEBRA system division. It contains some tables, as well as the Input/Output buffers for HRIN and HROUT.

      COMMON/PAWC/NWPAW,IXPAWC,IHDIV,IXHIGZ,IXKU,FENC(5),LMAIN,HCV(9989)

      DIMENSION IQ(2),Q(2),LQ(8000)
      EQUIVALENCE (LQ(1),LMAIN),(IQ(1),LQ(9)),(Q(1),IQ(1))
           
 

Figure:  The layout of the /PAWC/ dynamic store

 [FPAWSTOR]

The use of ZEBRA

Inside the HBOOK division the various data elements are stored as a ZEBRA data structure, one for each ``identifier''. In fact all identifiers (histogram or Ntuple numbers) are stored in an ordered array in a ZEBRA bank and access to the information associated with the HBOOK data is via the reference link at the same offset as the identifier in the data part of the bank. The data structure for a given element depends on its characteristics. In any case the top bank for a given element contains the title and other constants, while the data themselves are stored in another bank hanging from the previous one. Sometimes other banks are created, e.g. for automatic binning, for storing the limits of the elements of a Ntuple and, when a Ntuple is kept in memory, for containing the overflow of the data, for projections, slices and bands in the 2-dim case of for containing the errors associated to a bin. This means that each HBOOK identifier has a whole set of attributes associated with its existence, and when a histogram or Ntuple is written to backup store and later reread, the complete data structure, containing all characteristics and attributes are retrieved. Figure [more info] shows the ZEBRA data structure for a two-dimensional histogram. The precise layout of this bank should be of no concern to the user. It is only shown here as an example of the underlying ZEBRA structure of HBOOK. Note the use of the data part of the bank for storing attributes (e.g. title, number of bins, number of entries) as well as of the link part for storing the addresses to access the associated data points (scatter plot contents, X and Y projections, slices and bands and their associated errors).

Figure:  The ZEBRA data structure used for two-dimensional
histograms

 [FZEBRA]