Basant Dagar <dagar.basant2@xxxxxxxxx> writes: > I have big flat table with 100 columns in it. For about 40% of its data, 90 > columns would be null out of 100.And this table keeps growing and will > initial have more than 100 million rows. > â??May I know, will this impact the size in anyways as I heard nulls will > take no or very little space in PostgreSQL unlike oracle. even for millions > of rows with many columns in it. Is that true? If a row has any nulls at all in it, there is a "nulls bitmap" added to the row header which contains 1 bit per column, showing whether that column is null or not. Null columns do not occupy any space in the actual payload area. A row with no null columns omits the bitmap. So, if you like, you can consider that the first null appearing in a row of this table will cost you 16 bytes (100/8 = 12.5 rounded up to the next alignment boundary), and then all the rest are free. > â??And if that is not true, would you recommend to make this table into 2 > tables with the 2nd table containing those â??40% records with only 10 > required columns in it? It seems highly unlikely that such a scheme would be worth the trouble. regards, tom lane -- Sent via pgsql-admin mailing list (pgsql-admin@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-admin
