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Version 1.9 Build 1367

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Subsections

• Software Installation
• Data Sizes

Disk Space

Software Installation

Disk space is relatively inexpensive, so the amount of disk space required to hold an AIPS++ installation should not be a serious obstacle. (The effect on memory use is serious and is discussed later). It will be embarrassing if it takes too much disk space however (more than, say, a few hundred Megabytes).

Data Sizes

Images should not be intrinsically much larger in AIPS++ than in any other system since the size is so dominated by the pixel data. (That is, the ratio of data to ``book-keeping'' is inherently high). Moreover, the scaled storage manager allows us to transparently use scaled 2-byte integers if we choose to.

The main danger comes about because our Measurement-Equation based processing is inherently for all polarizations at once. The software must be able to store on disk only those polarizations which are required, not insist on always writing 4-polarization images. Similar arguments occur for visibility data.

Danger 3

Only store the desired (or required) polarizations in persistent data.

The raw MeasurementSet (visibility data) is more susceptible to general data bloat since the ratio of book-keeping (indices into subtables, for example) to correlation data might be high, particularly for continuum data. Moreover optimizations such as assuming that a single number can represent the weight of an entire visibility spectrum are made in other packages and will be expected in AIPS++². These sorts of problems should be solvable by using and creating appropriate storage managers.

Danger 4

Generality in the MeasurementSet might cause data bloat for the ``usual'' cases.

We certainly can't afford an integral factor bloat in the raw data size. Even a 20% factor would be painful for large experiments that might already barely fit on a single disk.