Home/ Questions/Q 7416893
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-29T07:35:25+00:00

I have 2 processes that connect to the same DB. The first one is

  • 0

I have 2 processes that connect to the same DB.
The first one is used to read from the DB and the second is used to write to the DB.
The first process sends write procedures for executing to the second process via message-queue on linux.

Every SQL-statement is taken in the prepare, step, finalize routine; Where the prepare and step are made in loop of 10000 times till it succedd (did this to overcome DB locked issues).

To add a table i do the next procedure:

  1. the first process sends request via msg-q to the second process to add a table and insert garbage in it’s rows in a journal_mode=OFF mode.

  2. then the first process checks for the existing table so it could continue in its algorithm. (It checks it in a loop with usleep command between iterations.)

The problem is that the second process is stuck in the step execute of ‘PRAGMA journal_mode=OFF;’ because it says the DB is locked (Here too, i use a loop of 10000 iterations with usleep to check 10000 time for the DB to be free, as i mentioned before).

When i add to the first process in the ‘check for existing table’ loop, the operation of closing the connection, the second process is ok. But now when i add tables and values sometime i get ‘callback requested query abort’ in the Step Statement.

Any help of whats happening here ?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    Use WAL mode. It allows one writer and any number of readers without any problems. You don’t need to check for the locked state and do retrys etc.

    WAL limitation: The DB has to be on the local drive.

    Performance: Large transactions (1000s of inserts or similar) are slower than classic rollback journal, but apart of that the speed is very similar, sometimes even better. Perceived performance (UI waiting for DB write to finish) improves dramatically.

    WAL is a new technology, but already used in Firefox, Adroid/iOS phones etc. I did tests with 2 threads running at full speed – one writing and the other one reading – and did not encounter a single problem.

    You may be able to simplify your app when adopting the WAL mode.

    • 0