sqldb and threads
lazarus / 16-Databases

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Max V. Terentiev · 2017-06-28 12:29

Hi,

I need to read/write SQLite database from several threads.

Should I create TSQLite3Connection in each thread ?

Or I can use single connection in many threads ? Should I use
CriticalSections in this case ?

Thanks for help !

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Blestan · 2017-06-28 14:21

not all functions of sqlite are thread safe .... create several
connections in a pool and use them in the threads... do not use
critical sections on one connection because if the app is heavely db
active you will loose the advantages of multithreading ...
one possible solutions is to serialize the access to sqlite in one
thread and use a event mechanisme to signal the threads that the db
operations are executed ...

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Max V. Terentiev · 2017-06-28 15:23

Sqlite have different compile-time threading options, including
serialized where one connection can be shared betweern threads and
multithreaded where each thread must have own connection.

But what about sqldb ? Is it threadsafe ?

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Blestan · 2017-06-28 16:46

no idea about sdldb... why not use raw sqlite.dll? you can take a look
at rqlite witch is a distribited sqlite and acess i rest based

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Leledumbo · 2017-06-30 20:57

Quote from: Max V. Terentiev on June 28, 2017, 05:23:01 pmBut what
about sqldb ? Is it threadsafe ?
AFAIK it just relies on the underlying DBMS.

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taazz · 2017-06-30 21:16

Quote from: Leledumbo on June 30, 2017, 10:57:58 pmQuote from: Max V.
Terentiev on June 28, 2017, 05:23:01 pmBut what about sqldb ? Is it
threadsafe ?
AFAIK it just relies on the underlying DBMS.
That is not enough. For example lcl relies on the underline widgetset
as well but it is not thread safe, even when the underline widgetset
is.

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Max V. Terentiev · 2017-07-03 12:15

But in the end. Should I create should I create TSQLite3Connection in
each thread ? Or I can use (in threads) single connection from main
DataModule ?

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mangakissa · 2017-07-04 06:26

You have to create TSQLite3Connection in each thread.
But be carefull. As I mentioned earlier, I don't know is the database
will be locked for another transaction is the database is opened.

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Max V. Terentiev · 2017-07-06 11:22

Thanks for help !