IBM MAINFRAME HELP & SUPPORT FORUMS

monasu1998 · Joined: 23 Dec 2005 Posts: 96 Location: Hyderabad

Hi Frens:

Both the READ LOGICAL and FIND are useful in someway or other way.
But my DBA told me to use READ LOGICAL instead of FIND?
Can anyone plz clarify the significance of this instruction?

Dariusz · Joined: 11 Aug 2005 Posts: 27 Location: POLAND

Hi.
Find is more usable bycause it runs by ADABAS and it is quickly.
There is one problem only:
for FIND WITH .... we need descriptor field,but too much descriptors
is not better for quick working.
Regards.

toughmetals · Joined: 10 Jan 2006 Posts: 14 Location: India

Hi,

Their is quite difference in processing of READ and FIND.

FIND:
1. Search the inverted list for Descriptor value
2. Build a list of ISN with the matched value
3. Process the ISN thru address converter to fetch the physical record
4. Repeat 3. until ISN list exhaust

READ Logical:
1. Search the inverted list >= Descriptor value and get the ISN
2. Process the ISN and get the actual record
3. Repeat 2. until Inverted list exhaust or u'll get some escaping criteria.

You see, the difference lies here is building of ISN list in case of FIND in working storage. Which is overhead.

Next major difference is we use READ logical only in case we want to get the data sorted by some descriptor value. Whereas, FIND will give us the data in order ISN site in the inverted list.

Borebeat · Joined: 16 Jan 2006 Posts: 7 Location: Coimbatore

Its better to think of READ as for SEQUENTIAL READ and FIND for RANDOM ACCESS.

toughmetals · Joined: 10 Jan 2006 Posts: 14 Location: India

Hi BB,

"FIND for RANDOM ACCESS". Could you pls give me some examples?

So that we will be more clear.

Borebeat · Joined: 16 Jan 2006 Posts: 7 Location: Coimbatore

FIND do not actually read the database; ISNs are read directly from the Associator's inverted lists.

READ commands are used to read actual records from Data Storage. Depending on the specified command and its options, records are read individually

1. in the sequence in which they are stored; (READ PHYSICAL)

2. in the order of an ISN list created by one of the database query commands; or (READ BY ISN)

3. in logical sequence according to a user-specified descriptor. (READ LOGICAL)

FIND is faster than READ !!!! :-)

toughmetals · Joined: 10 Jan 2006 Posts: 14 Location: India

Hi BB,

After Fetching ISN from the Inverted list it will go to Address converter to take the RABN number, after that it will get the actual record from DATABASE.

Only Histogram will not get into the DB and read the information only from Inverted List.

Thanks,
Deeps