A NULL costs almost nothing, in anycase, less than a real value. There is the cost of the NULL bitmap, 1 bit per column for each column if there are *any* NULLs in a row, but once you'ce got one, the rest are free for that row. This is in the documentation somewhere... On Fri, Apr 02, 2004 at 12:18:47PM -0500, Randall Skelton wrote: > What is the storage cost of a null entry in a column? i.e. does a null > entry of type integer, float8 or text consume the same amount of > storage as one that is filled? I ask because I have satellite data > which is transmitted via a dodgy RF link that drops data packets. This > means I have a number of columns in a table that are null. Moreover, > the operations people decided to use a compression scheme whereby > non-changing bit/integer values are not output at regular intervals > which also adds a considerable number of null entries into the columns. > Because of this, we made a decision that we would have hundreds of 2 > column tables (timestamp, value) and use unions, intersections, and > joins to get what was needed. Unfortunately, this has made application > programming a real nightmare as we are often forced to reconstruct a > snapshot frame for the range of times either in C or have the app > create temporary tables in SQL and insert the relevant data prior to > selecting it. As it stands, we've ordered a new disk array and > provided that the storage costs are not that high, I will probably be > reorganising all this next week. If anyone has any other suggestions, > I'd be very keen to hear them. > > Cheers, > Randall > > > ---------------------------(end of broadcast)--------------------------- > TIP 2: you can get off all lists at once with the unregister command > (send "unregister YourEmailAddressHere" to majordomo@postgresql.org) -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > This space intentionally left blank
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