Why not a read lock?

Question

Hi,
I use dbsql operate the database, when i begin a transaction, followed by executing a query, by observing its lock and found it produced a write lock, instead of reading a lock?
Why is it? Do the following:
[root@iZ28aslsffdZ db_sql]# dbsql test.db
Berkeley DB 12c Release 1, library version 12.1.6.1.19: (June 10, 2014)
Enter ".help" for instructions
Enter SQL statements terminated with a ";"
dbsql> create table t (a int);
dbsql> insert into t values (1),(2),(3);
dbsql> begin;
dbsql> select * from t where a = 1;
1
[root@iZ28aslsffdZ test.db-journal]# db_stat -CA
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Lock conflict matrix:
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
80000014 dd= 0 locks held 1
write locks 1
pid/thread 30420/140133200996096 flags 0
priority 100  
80000014 WRITE    
3 HELD      
test.db:table00003 database  
0

Answer 1

That is expected behavior.  It is due to an internal optimization for single threaded access to the database.  The first time two threads clash trying to get access to the database schema table (which is what table00003 is), the database will stop getting a write lock on the table and will instead just get a read lock.
Lauren Foutz