Can some one tell me a better way...

Question

Hi All..
I work on a web application. I create user ids for people logging into my application. here I have a small problem.. This is what I am currently doing...
When I create a new user, I assign a new user id to the user and store all hi info.
All our user ids are stored in User_ID table and user info in User_Info table.
First I get the max user id from the User_Id table.
int iuserid = select max(User_ID) from User_ID;
Then I add ' 1 ' to this and assign it to new user.
iuserid = iuserid+1;
insert into User_id values(iuserid, <ssn> );
Then I store all user info in User_info table..
insert into User_info(iuserid, <first_name>, <last_name>,...);
Both these SQLs are executed as a transaction.
The problem that I have...
It works fine in a normal environment and in my testing.
But when the load inceases, before I insert into the User_info, another user tries to get the max User_id from User_ID table, then it conflicts..
I have seen occurences of User_Info storing the info of a different user against the User_id when many people are accessing the app at the same time.
Can some one tell me a better way to handle this scenario..
Appreciate all you help..
TIA..
CK

Answer 1

Hi,
assuming that the requirement for user_id is only for uniqueness (primary key requirement) not continuosly.
perhaps can try this,
1) create a table to keep the max id for each table's key.
e.g.
create table key_id_lookup
key_name char(n),
current_value number(m)
where n & m is the size of the field
2) for each creation of entry in the user_id table, lookup the value in the key_id_table and increment it after retrieval.
e.g. current_id = select current_value from key_id_lookup where key_name = 'user_id_key';
current_id+=1;
update key_id_lookup set current_value = current_id where key_name = 'user_id_key';
something similar to use of sequence if your database support it.
3) continue with the creation of record in other tables. now obtain the time stamp of creation and append with the current_id obtained. e.g. timestamp = 132456872; size of m is 5, user_id = 132456872 x 100000 + current_id;
this should give you a unique key at creation time.
There should be other better ways of resolving this(like locking the table for the update operation but affect performance, etc), depending on the feature supported by the database in use.
Hope this can help as last resort if other options not available.