Avoid deadlock on Firebird - .net-core

Question

I would like to avoid DeadLock issue in code. I read the way is to use FOR UPDATE WITH LOCK also FbTransactionBehavior.Wait. But my second transaction, despite it is waiting for the first one to finish, always dies by DeadLock.
I wrote a very simple test to illustrate my issue, I pasted the test here below, easier than trying to explain with words (I guess)
The goal is to complete both transactions. The test result is a bit bizarre, the second transaction waits until the first one finishes but also dies. I expect both transactions completes (if it is possible)
tx1
tx2
Comments
tx starts
_ 
_ 
_ 
tx starts
_ 
Read id=6
_ 
_ 
Update id=6
_ 
_ 
_ 
Read id=6
<- tx2 Locked, it's ok, waiting for commit
Commit
_ 
<- tx2 unlocked
_ 
_ 
<- tx2 deadlock :(
using FirebirdSql.Data.FirebirdClient;
namespace fireb;
public class UnitTest1
{
[Fact]
public void Test1()
{
// tx 1 starts
using var connection1 = new FbConnection("database=localhost:demo.fdb;user=sysdba;password=masterkey");
connection1.Open();
using var transaction1 = connection1.BeginTransaction(
new FbTransactionOptions() { TransactionBehavior = FbTransactionBehavior.Wait, WaitTimeout = TimeSpan.FromSeconds(5) });
// tx 2 starts
using var connection2 = new FbConnection("database=localhost:demo.fdb;user=sysdba;password=masterkey");
connection2.Open();
using var transaction2 = connection2.BeginTransaction(
new FbTransactionOptions() { TransactionBehavior = FbTransactionBehavior.Wait, WaitTimeout = TimeSpan.FromSeconds(30) });
// updating on tx1
using var command_pre1 = new FbCommand("select * from demo where id = 6 FOR UPDATE WITH LOCK;", connection1, transaction1);
command_pre1.ExecuteReader().Read();
using var command1 = new FbCommand("update demo set foobar = 'pp1' where id = 6;", connection1, transaction1);
command1.ExecuteNonQuery();
// commit in 10''
Action myCommit = () => {
transaction1.Commit();
transaction1.Dispose();
command_pre1.Dispose();
command1.Dispose();
connection1.Close();
connection1.Dispose();
};
var aTimer = new System.Timers.Timer(10000);
aTimer.Elapsed += (a,b) => myCommit();
aTimer.AutoReset = false;
aTimer.Enabled = true;
// updating tx2
using var command_pre2 = new FbCommand("select * from demo where id = 6 FOR UPDATE WITH LOCK;", connection2, transaction2);
command_pre2.ExecuteReader().Read(); // <--- here dies. How to avoid?
using var command2 = new FbCommand("update demo set foobar = 'pp2' where id = 6;", connection2, transaction2);
command2.ExecuteNonQuery();
// Commit tx 2
transaction2.Commit();
}
This is the error:
FirebirdSql.Data.FirebirdClient.FbException : deadlock
update conflicts with concurrent update
concurrent transaction number is 67
---- FirebirdSql.Data.Common.IscException : deadlock
update conflicts with concurrent update
End of question
If you want to reproduce:
To create the table ...
// from here just arranging database and data
public UnitTest1()
{
// Just to create database, table and row
// CreaBd();
// CreaTaula();
// InsertData();
}
private static void CreaTaula()
{
using var connection = new FbConnection("database=localhost:demo.fdb;user=sysdba;password=masterkey");
connection.Open();
using var transaction = connection.BeginTransaction(System.Data.IsolationLevel.RepeatableRead);
using var command = new FbCommand(
"create table demo (id int primary key, foobar varchar(20) character set utf8); ",
connection, transaction);
command.ExecuteNonQuery();
transaction.Commit();
}
private static void InsertData()
{
using var connection = new FbConnection("database=localhost:demo.fdb;user=sysdba;password=masterkey");
connection.Open();
using var transaction = connection.BeginTransaction(System.Data.IsolationLevel.RepeatableRead);
using var command = new FbCommand(
"insert into demo values (6, 'FooBar');",
connection, transaction);
command.ExecuteNonQuery();
transaction.Commit();
}
private static void CreaBd()
{
FbConnectionStringBuilder builder = new FbConnectionStringBuilder();
builder.DataSource = "localhost";
builder.UserID = "sysdba";
builder.Password = "masterkey";
builder.Database = "demo.fdb";
builder.ServerType = FbServerType.Default;
FbConnection.CreateDatabase(builder.ConnectionString);
}
}
If you want to run firebird in docker
docker run -d \
--name firebird \
-p 3050:3050 \
-e "ISC_PASSWORD=masterkey" \
-v /Users/dani/tmp/fireb/dockerdb:/databases \
jacobalberty/firebird