Hello, hackers. Any body know how to produce a Soft Block case of Deadlock Detection? I have produced the Hard Block case, but can't produce the Soft Block case.
I read the design: src/backend/storage/lmgr/README. It reads, "If a process A is behind a process B in some lock's wait queue, and their requested locks conflict, then we must say that A waits for B, since ProcLockWakeup will never awaken A before B. This creates additional edges in the WFG. We call these "soft" edges, as opposed to the "hard" edges induced by locks already held. Note that if B already holds any locks conflicting with A's request, then their relationship is a hard edge not a soft edge." But after trying many testing, I couldn't figure out how to produce a Soft Block. Following is what I did. * Hard Block Case ** Prepare create table t1 ( id int primary key, test int ); create table t2 ( id int primary key, test int ); insert into t1 values (10,10); insert into t2 values (20,20); ** test step1/backend1: begin; update t1 set test=11 where id=10; step2/backend2: begin; update t2 set test=21 where id=20; step3/backend1: update t2 set test=21 where id=20; step4/process2: /*deadlock detected*/ update t1 set test=11 where id=10; * Soft Block Case ** Prepare create table t1 ( id int primary key, test int ); create table t2 ( id int primary key, test int ); create table t3 ( id int primary key, test int ); insert into t1 values (10,10); insert into t2 values (20,20); insert into t3 values (30,30); ** test step1/backend1: /*lock t1.row1*/ begin; select * from t1 where id=10 for update; step2/backend2: /*lock t2.row1*/ begin; select * from t2 where id=20 for no key update; step3/backend3: /*lock t2.row1*/ begin; select * from t2 where id=20 for key share; step4/backend4:/*lock t3.row1*/ begin; select * from t3 where id=30 for update; step5/backend4:/*try to lock t1.row1*/ update t1 set id=11 where id=10; step6/backend3:/*try to lock t3.row1*/ update t3 set id=31 where id=30; step7/backend5:/*try to lock t2.row1, hope to create a soft edge*/ begin; update t2 set id=21 where id=20; step8/backend1:/*try to lock t2.row1*/ /*Expect to detect soft block, but there seems no soft block*/ update t2 set test=21 where id=20;