B4J Question RDC2 and SQLITE_IOERR

[marcick]

Sometimes happens that on my RDC2 app I have this error

(SQLException) java.sql.SQLException: [SQLITE_IOERR]  Some kind of disk I/O erro
r occurred (disk I/O error)

Still have to understand the code line that generate the error.
Any vague idea about this ?
When I fall in this situation the error then happens continuously and to solve I have to restart the app

 

[Erel]

SQLite engine is more fragile when it comes to concurrent access.

You have two options:
1. Limit the connection pool size to 1: https://www.b4x.com/android/forum/threads/jrdc2-with-sqlite-need-help-with-wal-pool.71145/#content
2. Change jRDC2 to use jSQL directly without the pool (and switch to WAL mode): [WebApp] Concurrent access to SQLite databases
Make sure to initialize jSQL with InitializeSQLite.

 

[marcick]

Thank you. I see I have two timers that contains "con1 = rdcConnector1.GetConnection" (con1 is public).
So: if timer1 execute that statement and before it close the connection timer2 do the same i fall in the above error ?
is this situation called "concurrent access" ?

 

[Erel]

Have you modified jRDC2? What changes have you made?

Concurrent access will mainly happen when two clients send requests at the same time. This will be solved by limiting the pool size.

 

[marcick]

Yes Erel, I have integrated JRDC2 with the PushServer but it's difficult now to see what is chenged.
Is this all is needed to solve ?

'Initializes the object. You can add parameters to this method if needed.
Public Sub Initialize
    Config = LoadConfigMap
    pool.Initialize(Config.Get("DriverClass"), Config.Get("JdbcUrl"), Config.Get("User"), _
        Config.Get("Password"))
#if DEBUG
    DebugQueries = True
#else
    DebugQueries = False
#end if   
    serverPort = Config.Get("ServerPort")
    LoadSQLCommands(Config)
    Dim jo As JavaObject = pool  ' added line
    jo.RunMethod("setMaxPoolSize", Array(1))  ' added line
    jo.RunMethod("setMinPoolSize", Array(1)) ' added line
End Sub

 

[Erel]

Yes, assuming that you are only accessing the database through the connection pool.

 

[marcick]

Ok, let's see what happens now.
No need to switch to WAL mode, right ?

 

[marcick]

I have this warning in the log

WARNING: Bad pool size config, start 3 > max 1. Using 1 as start.

and this error also ...

java.lang.RuntimeException: java.sql.SQLException: An attempt by a client to checkout a Connection has timed out.

 

[Erel]

No need to switch to WAL mode, right ?

It is better to switch to wal mode.

Ignore the warning.

About the error, make sure to always close the SQL object received from the connection pool as soon as possible.

 

[marcick]

be patient ..... I'm no longer a fresh mind

Everywhere I have a getconnection I have to set the WAL ?

con1 = rdcConnector1.GetConnection
con1.ExecNonQuery("PRAGMA journal_mode = wal")

' do what I need

If con1 <> Null And con1.IsInitialized Then con1.Close

 

[Erel]

Everywhere I have a getconnection I have to set the WAL ?

No. Only once after you initialize the pool.

You don't need to check whether con1 is null or initialized. It will be initialized at that point.

 

[marcick]

I'm becoming crazy

This is my App_Start

Sub AppStart (Args() As String)
    rdcConnector1.Initialize
    con1 = rdcConnector1.GetConnection
    con1.ExecNonQuery("PRAGMA journal_mode=WAL")

And this is the log

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'PRAGMA journal_mode=WAL' at line 1

Where I'm wrong ?

 

[Erel]

What is RDC connected to? SQLite database or MySQL database?

 

[marcick]

MySQL

 

[Erel]

I think that the whole discussion here is incorrect. If the error is related to SQLite and RDC is connected to MySQL then the error is not related to RDC at all. It is related to something else.

 

[marcick]

You're right, I'm in total confusion. But WAL mode is related only to SqLite, not MySQL, right ?

 

[Erel]

But WAL mode is related only to SqLite, not MySQL, right ?

Right.