non-consistent multi-thread data

[vitya tsoi]

non-consistent data on three or more threads. 

result of code exmple is

MISS: 300

TOTAL: 279

why?

 

char const* dbpath = "/tmp/sophia";


void* env = sp_env();
sp_setstring(env, "sophia.path", dbpath, 0);
sp_setstring(env, "db", "test", 0);
void* db = sp_getobject(env, "db.test");
sp_open(env);
 
int id = 1;
int NREPEAT = 100;
int NTHR = 3;
 

auto lexec = [&](int idx) {
 

 for (int i = 0; i < NREPEAT; ++i) {
   int rc = 0;
   
   do {

     void *tx = sp_begin(env);
     void *o = sp_document(db);
     sp_setstring(o, "key", &id, sizeof(id));

     int v = 0;

     if ((o = sp_get(tx, o))) {
        v = *(int*)sp_getstring(o, "value", nullptr);
        sp_destroy(o);
     }

     v++;
 
     o = sp_document(db);
     sp_setstring(o, "key", &id, sizeof(id));
     sp_setstring(o, "value", &v, sizeof(v));
     sp_set(tx, o);
 

     // on lock
     // do rc = sp_commit(tx); while (2 == rc);

     // or ignore lock
     rc = sp_commit(tx);
     if (2 == rc) sp_destroy(tx);
 

     if (rc < 0) {
       char* err = (char*)sp_getstring(env, "sophia.error", nullptr);
       fprintf(stderr, "err: %s", err);
       free(err);
       exit(1);
     }

    } while (rc);

  } // repeat

 };
 

 std::thread th[NTHR];
 
 for (int i = 0; i < NTHR; ++i) {
   th = std::thread(lexec, i);
 }
 
 for (int i = 0; i < NTHR; ++i)
   th[i].join();
 
 void *o = sp_document(db);
 sp_setstring(o, "key", &id, sizeof(id));

 int v = 0;
 if ((o = sp_get(db, o)))
   v = *(int*)sp_getstring(o, "value", nullptr);

 sp_destroy(o);
 sp_destroy(db);
 sp_destroy(env);
 

 printf("MISS %d", NTHR * NREPEAT);
 printf("TOTAL %d", v);
 assert((NTHR * NREPEAT) == v);
}
 

[Dmitry Simonenko]

I've made a mistake in the prepare logic of the commit. Sorry for that.

Fixed by commit:

https://github.com/pmwkaa/sophia/commit/cc60da5cef3dfde973ab8ddf8b3ac0bf4ec09522

Your test case has been added to the test code base:

https://github.com/pmwkaa/sophia/blob/master/test/multithread/multithread.test.c#L225

Thanks for your time.

[vitya tsoi]

Excellent! Thank you!

what about case on lock

 do rc = sp_commit(tx); while (2 == rc);

commit return 1 if parallel  locker transaction is commited (data changed) and 0 if escaped?


суббота, 9 апреля 2016 г., 21:17:37 UTC+3 пользователь Dmitry Simonenko написал:

[Dmitry Simonenko]

Ok, the idea behind commit status is following:

status = sp_commit(tx)

(0) transaction commited:

all data has been successfully written to the storage.

the transaction is no longer exists.

(1) transaction forced to rollback on commit:

conflicting data has been changed by other commited transaction.

the transaction is no longer exists.

(2) in-lock

the transaction is in conflict by some other active transaction.

the transaction is exists.

Basically this status means that sp_commit(tx) should be retried later. In case if the conflicting transaction

(or all of them) are aborted for some reason, then transaction yet has a chance for 

successfull commit.

Following status can be used to implement an appllication specifics timeout,

resolve deadlocks, etc.

(-1) transaction forced to rollback on error

disk error, out-of-memory, etc.

the transaction is no longer exists.