"index size"

["Shulzhenko Vasyl" <vasilis@softline.kiev.ua>]

>On Tue, 30 Mar 1999 stuartk@au1.ibm.com wrote:
>
>> For some time now, I have been intrigued about the "index size" which
>is
>> reported by the supplied utilities such as dbschema and dbexport.
>> 
>> For example:
>> 
>> { TABLE "dba".table1 row size = 81 number of columns = 3 index size =
>12 }
>>
>^^^^^^^^^^^^^^^
>> create table "informix".notes
>>   (
>>     integer1 integer,
>>     smallint1 smallint,
>>     char1 char(75)
>>   );
>> revoke all on "dba".notes from "public";
>> 
>> create index "dba".table1_idx on "dba".notes (integer1);
>> 
>> >From my understanding in the manuals, the to calculate the size of
>the
>> index,
>> it is the (length of the fields in the index) + 4, so theoretically I
>was
>> expecting to see 8 as the index size (integer length 4 + 4).
>> 
>> After some fiddling, trying out different indexes etc. and seeing what
>> dbschema was reporting in each case, a formula has come to light of
>how
>> the utilities calculate their reported amounts.
>> 
>> This formula is as follows, where k = sum(length of each field in
>index):
>> 
>> index size = k + int(k/2) + 6
>> 
>> This works with every table in our schema.
>> 
>> Just out of curiosity, I was wondering if anyone can enlighten me as
>to why
>> this formula is used by the utilities, since I cannot relate it back
>to the
>> manuals in any way at all ?
>> 
>> --StuK.
>> 
>> 
>
>Stuart,
>I asked the same question about a month ago and got only 1 response.
>I'm not sure to the accuracy of the answer so I will just include the
>message sent to me.
>
>>Hi, Joseph:
>>
>>I'm not sure if you ever got an answer to your newsgroup question, but
>the
>>size
>>of an index entry is :
>>
>>key size + rowid + delete flag + slot entry
>>
>>key size  -- in your example (integer), this is 4 bytes
>>rowid is 4 bytes
>>delete flag is 1 byte
>>slot entry is 4 bytes
>>
>>So, in your case, the math would be:
>>
>>4 + 4 + 1 + 4 = 13
>>
>>Perhaps (i.e., I don't know for sure) dbschema does not report the 1
>byte
>>taken  up by the delete flag.
>>
>>HTH
>>
>>--Jeff 
>>
>>===========================================================
>>Jeff Tyzzer
>>Senior Consultant
>>Data Warehouse Consulting Practice
>>Informix Software, Inc.
>>Phone: (916) 491-1262
>>E-mail: jtyzzer@informix.com
>>===========================================================
>
>This might shed some light on the subject or maybe someone else can
>help. Because I've never heard of a delete flag in Informix or slot
>entry.
>
>Joe
>------------------------------------------------------------------------
>-
>Joseph Cullipher <joseph@cannonexpress.com> Standard Disclaimers Apply
>------------------------------------------------------------------------
>-
>