Sequence caching with oracle

Question

Hi,
In my application, I use toplink as a JPA provider. For performance reasons, I defined an allocationSize on sequence generator for some persistence objects. I read some documentation to understand how it works, the result of my research is that the allocationSize of sequence generator must match with the increment value of the sequence in database.
So here is my question, what if my sequence define a cache in the database ? For a cache of 1000 values on the application (or server) side, I can create a sequence like this : sequence myseq increment by 1000 cache 20.
Does it mean that 20 values will be cached or 1000*20 values will be cached ? Is the cache size defined per session or for all the sessions of the database ?
Thanks.
Will.

Answer 1

ok.... so if my sequence starts with 10000 and has a cache of 5, values from 11000 to 15000 will be cached, not values from 10000 to 100020 ?"5" values will be cached. You will find the following example to be helpful.
[cache]
SQL> create sequence myseq start with 10000 cache 5;
Sequence created.
SQL> select increment_by, cache_size, last_number from user_sequences where sequence_name = 'MYSEQ';
INCREMENT_BY CACHE_SIZE LAST_NUMBER
1 5 10000
SQL> select myseq.nextval from dual;
NEXTVAL
10000
SQL> /
NEXTVAL
10001
SQL> /
NEXTVAL
10002
SQL> /
NEXTVAL
10003
SQL> /
NEXTVAL
10004
SQL> select increment_by, cache_size, last_number from user_sequences where sequence_name = 'MYSEQ';
INCREMENT_BY CACHE_SIZE LAST_NUMBER
1 5 10005
SQL> select myseq.nextval from dual;
NEXTVAL
10005
SQL> select increment_by, cache_size, last_number from user_sequences where sequence_name = 'MYSEQ';
INCREMENT_BY CACHE_SIZE LAST_NUMBER
1 5 10010
SQL>
Asif Momen
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