-
Maximum number of columns in table
All,
I remember, if total number columns reach to N in a table, oracle would not store the record in the same data block. I don't remember the value N. Can any one answer for this?.
Regards
GT
-
Originally Posted by pranavgovind
All,
I remember, if total number columns reach to N in a table, oracle would not store the record in the same data block. I don't remember the value N. Can any one answer for this?.
Regards
GT
1000 max.
"What is past is PROLOGUE"
-
Anything over 255 is chained.
-
David is right its is 255.Over 255 the rows are chained
-
But in this case chained doesn't mean that the data are not all stored in the same block
-
Originally Posted by slimdave
Anything over 255 is chained.
It is not chained. The data of the columns whose number is > 255 is still stored in the same block provided the block has space.
The real problem is "table fetch continued row " event appears in the statspack report.
Oracle has to do 2 IOs (logical) for the data appears after the 255th column even when all the columns data are stored in one block and the row is fetched via index look up.
However, full table scan will not suffer from 2 IOs.
You can have 1000 columns in a table. In my opinion, restrict the number of columns less than 255 and the performance will be good.
Tamil
Tamil
-
Originally Posted by tamilselvan
It is not chained. The data of the columns whose number is > 255 is still stored in the same block provided the block has space.
Tamil
Will the block size 2k ~ 32k has more ~ less impact with the number of I/O's for columns > 255?
"What is past is PROLOGUE"
-
Originally Posted by dbasan
Will the block size 2k ~ 32k has more ~ less impact with the number of I/O's for columns > 255?
The block size does not matter.
Tamil
-
It's a real learning experience this, ain't it?
-
As long as an object has proper storage attributes defined and its row fits within a block, there shouldn't be any issues. Row migration and Row chaining caused either by a row update or inability to accomodate a row within a block can cause waits. You can find details on row migration, row chaining and the specific conditions that cause the "table fetch continued row" wait event, at these links:
http://www.akadia.com/services/ora_chained_rows.html
or
http://www.oracle.com/technology/ora...o62asktom.html
http://www.dbaxchange.com
Posting Permissions
- You may not post new threads
- You may not post replies
- You may not post attachments
- You may not edit your posts
-
Forum Rules
|
Click Here to Expand Forum to Full Width
|