I had cases where a small-transaction executed from multi-threads took relatively long time.
This happens to me only on Mac.
Same code on Windows is working very fast.

Environment:

• sqlite version: 3.28.0
• OS: Mac High Sierra 10.13.6
• IDE: xcode Version 10.0 (10A255)
• SQLite configuration:
  • Multi-threading mode (SQLITE_THREADSAFE==2).
  • One connection per-thread.
  • WAL-journal with synchronous set to NORMAL.

I noticed that while performing transaction from multiple-threads, sqlite enters sleep from the following stack:

• sleep ()
• unixSleep ()
• sqlite3OsSleep ()
• walTryBeginRead ()
• sqlite3WalBeginReadTransaction ()
• pagerBeginReadTransaction ()
• sqlite3PagerSharedLock ()
• lockBtree ()
• sqlite3BtreeBeginTrans ()
• sqlite3VdbeExec ()
• sqlite3Step ()
• sqlite3_step ()
• sqlite3_exec ("BEGIN IMMEDIATE TRANSACTION;")

What I noticed is that in these cases, and while halting the debugger, I could have few threads (3~5) in sleep while no other thread is active in sqlite code.
This is possible because the sleep is not an efficient-sleep, but rather full-sleep for hard-coded period of time (several micro seconds?).
This can cause a situation where after the blocking-thread did release database-lock, the other threads are not working yet as they are still asleep.

Sleep location in sqlite code:

static int walTryBeginRead(...){

    ...other code...

    if( cnt>5 ){
        int nDelay = 1;                      /* Pause time in microseconds */
        if( cnt>100 ){
            VVA_ONLY( pWal->lockError = 1; )
            return SQLITE_PROTOCOL;
        }

        if( cnt>=10 ) nDelay = (cnt-9)*(cnt-9)*39;
        sqlite3OsSleep(pWal->pVfs, nDelay);	 <--- THE SLEEP
}

My question:
Can I modify something in sqlite build flags in order to make these sleeps less often?

Thanks, PazO