Difference Between Cylinder Migrate and Cylinder Split

Database
Enthusiast

Difference Between Cylinder Migrate and Cylinder Split

Hi,

What is the difference between Cylinder Migrate and Cylinder Split?

Both will occur when Cylinder Full condition is countered.

>>>Cylinder Migrate — Checks the logically adjacent cylinders for fullness. If it finds room, it moves a maximum of 10 data blocks from the congested cylinder to an adjacent one.
>>> Cylinder Split — Looks for a free cylinder, allocates one, and moves a maximum of 20 data blocks from the congested cylinder to a new one.

Thanks,
Syed
4 REPLIES
Enthusiast

Re: Difference Between Cylinder Migrate and Cylinder Split

When the Cylinder is full, TD would first try to do a

Defragmentation.
Which means it will try to move all free blocks to the bottom of the cylinder. with some luck these contiguous free blocks can now be combined to make a large free block, which would fit the request.

If the above attempt also failed, then.

Cylinder migrate.
Here the logically adjacent cylinder is checked for space, if it has any then some (10?) blocks are moved from that cylinder.

If that didn't save either, then we go to

Cylinder Split.
Which requires free cylinders to be available. So a free cylinder is allocated to which about 20 blocks are moved to make space.

So what if we have no free cylinder

Mini Cylpack.
Ideally, this stage should not be reached, it just means that the Server is running short of space or the system is badly fragmented. (roll your eyes at the DBA).
This is almost like doing a defragmentation across the cylinders. so you try stacking cylinders by moving data blocks from the succeeding cylinders to the preceding cylinders till you finally get a cylinder "freed"

Enthusiast

Re: Difference Between Cylinder Migrate and Cylinder Split


Thanks

Cheers
Syed
Kks
Enthusiast

Re: Difference Between Cylinder Migrate and Cylinder Split

How to know there are not enough cylinders?
and
One cylinder can store upto

Enthusiast

Re: Difference Between Cylinder Migrate and Cylinder Split

"Not enough cylinders" means: "not enough free space"... For which you can just list the free space available per VProc (AMP).

In a typical configuration, a cylinder is made of 3872 sectors (having each secotr 512 bytes), which means 1.982.464 bytes per cylinder (roughly 1.9 Mb).

PS: I won't worry about cylinders: Teradata manages efficiently and transparently disk space allocation.