Hi,
Am using the API and having trouble (deadlock or crash) with multithreaded
access to a read-only sqlite3 file. Any help would be much appreciated.
- Running OSX with sqlite3 3.28.0 amalgamation compiled from code. Same
issue is occurring when the code is compiled for Windows using mingw64
- I have one sqlite3 db file holding one table of data of about 100k
rows and half a dozen columns with short-text or numeric data
- I have one process with two threads concurrently accessing the table:
- each thread has its own db connection
- each thread is running an identical "select x" query, many
thousands of time in rapid succession, with an indexed lookup, and only
retrieving 1 row (at most) of data
- I'm encountering a race condition and/or crash and have tried multiple
different ways to address
- Here are two approaches that are both failing:
- deadlock: both processes open db (once each before quering begins)
using SQLITE_OPEN_READONLY | SQLITE_OPEN_NOMUTEX |
SQLITE_OPEN_SHAREDCACHE.
The deadlock occurs in the btreeCursor function, which both threads
get stuck in (which in my version 3.28.0 amalgamation is on
lines 67576-67581)
for(pX=pBt->pCursor; pX; pX=pX->pNext){
if( pX->pgnoRoot==(Pgno)iTable ){
pX->curFlags |= BTCF_Multiple;
pCur->curFlags |= BTCF_Multiple;
}
}
- crash: both processes open db (once each before quering begins)
using SQLITE_OPEN_READONLY | SQLITE_OPEN_URI, with uri parameter
immutable=1. The crash occurs in sqlite3DbMallocRawNN, with a bad
memory access exception using lldb
I've tried other permutations of various flags that go along for
sqlite3_open_v2 , as well as setting pragma read_uncommitted, but can't
seem to get multi-threaded concurrent rapid-fire querying to work at all.
Am open to any changes to how the db is opened or sqlite3_step is called
etc.
Thoughts or suggestions? Seems like this should be a common use case so my
guess is the solution is easy and I've just got something wrong...
Thank you
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