Archives of the TeradataForum
Message Posted: Tue, 04 Jan 2011 @ 10:48:06 GMT
| Subj: | | Re: Basic teradata questions |
| |
| From: | | Anshuman.Singh |
Find your answer below
Regards,
Anshuman Singh
Cognizant
| | 1.) in case of NUSI "After the row hash of SI value is calculated the bynet will automatically active all the amps as per parsing
engines instructions. each amp locates the sutable rows containing the qualifying values and rowhash. this subtable rows contain the rowid for the
base rows, WHICH ARE GAUREENTED TO BE ON THE SAME AMP AS THE SUB TABLE ROWS ....." my question is why should the rowid's present on the same amp?
they can be on other amps | |
in case of NUSI the subtables are created on the same AMP that's why !!
| | 2.) this question may be silly but please answer me "if number of physical reads exceed the number of datablocks,then the optimizer
may decide that full table scan is faster" here what does it mean by physicalreads & datablocks | |
physicalreads & datablocks -- physicalreads may stand for values distinct values , typical rows per value teradata table consist of several
data blocks whenever a row is added to the end of data block When data rows begin being loaded or inserted each AMP allocates at least a 512 byte
sector inside a disk cylinder.
This 512 byte sector is considered a block of data
| | 3.) what are master indexes and cylinder indexes? | |
Cylinder Indexes was allocated at the beginning of every cylinder. Not sure about master indexes
| | 4.) does client attached network means loading client software on node? | |
Mainframes system serve as client attached.
Unix based systems serve for network attached
| | - how many primary indexes the table can contain?
>- on how many coloumns does we can specify primary index?
>- how many secondary indexes the table can contain?
>- on how many coloumns does we can specify secondary index?
>- maximum how many sessions does a P.E support?
>- max how many vprocs can a clique support? | |
As per v2r6 (64 columns in composite primary index)
32 columns for secondary index
120 sessions for PE
max how many vprocs can a clique support (that depends on node config )
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