1. Is there any limit in no of fields or limit in field size (Bytes) before issuing an end transaction command?
An Adabas file can have up to 926 fields and you can update all of them. Between End Transaction (ET) commands you must not overflow the hold queue. Ask your DBA for the value of NISNHQ - the maximum number of records you can place on hold (that is, Store, Update, or Delete).
2. I have an adabas file which has almost 500+ fields in it and if i want to update all the fields in a program will there be any problem?
Are many of the fields long alphanumeric, and are they full? If all the fields are 1 or 2 bytes, no problem. If most are A250, but contain only 1 or 2 characters, no problem. If many fields are A50 and are filled with 50 non-blank characters, you may have a problem.
The compressed record must fit into a physical Adabas block. Basically the compressed record length is the sum of all field lengths without leading zeros and trailing blanks. The block size is selected by the DBA based on several criteria. You will need to ask.
3. Is there any way to get to know the buffer size without the help of ADA DBA?
Not really. During execution of your Natural program, you can see the compressed record length in DBLOG, but for the block size, take a look at an ADAREP (Adabas report) or ask a DBA.