Re: Table with 300 columns (ie > 255) : Row Chaining ?

Hi Hemant,

> Your test table has 350 columns. A row piece can store at most 255
> columns. As a result, you have two row pieces: one with 255 columns and
> another with 95 (350-255) columns. As I wrote in my previous reply, the
> pieces are split and stored in "reverse order". That means two things:
> 1) the first row piece is the one having 95 columns 2) the first row
> piece is stored after the second one.

Just to add to this discussion, the answer is in the Concepts manual
(10gR2 Concepts - Chapter 5 Schema Objects):

When a table has more than 255 columns, rows that have data after the
255th column are likely to be chained within the same block. This is
called intra-block chaining. A chained row’s pieces are chained
together using the rowids of the pieces. With
intra-block chaining, users receive all the data in the same block. If
the row fits in the block, users do not see an effect in I/O
performance, because no extra I/O operation is required to retrieve
the rest of the row.

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