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Comment:In wal mode, if a "BEGIN EXCLUSIVE" command (or any other command that upgrades from no transaction directly to a write transaction) hits an SQLITE_BUSY_SNAPSHOT error, change the error code to SQLITE_BUSY to indicate to the caller that the condition may be transient.
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SHA3-256: 221ff63e7902226ebf728bb7442727420636831163708f360724506ce9487ab6
User & Date: dan 2018-07-05 15:46:55.944
Context
2018-07-05
17:03
Fix a typo inside an assert() statement introduced by the previous commit. (Closed-Leaf check-in: e335772847 user: dan tags: exp-busy-snapshot-fix)
15:46
In wal mode, if a "BEGIN EXCLUSIVE" command (or any other command that upgrades from no transaction directly to a write transaction) hits an SQLITE_BUSY_SNAPSHOT error, change the error code to SQLITE_BUSY to indicate to the caller that the condition may be transient. (check-in: 221ff63e79 user: dan tags: exp-busy-snapshot-fix)
2018-07-03
20:17
Test that a race condition can cause a "BEGIN EXCLUSIVE" to return SQLITE_BUSY_SNAPSHOT in wal mode. (check-in: 5a12db75d1 user: dan tags: trunk)
Changes
Side-by-Side Diff Ignore Whitespace Patch
Changes to src/btree.c.
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      if( pBt->nPage!=get4byte(&pPage1->aData[28]) ){
        rc = sqlite3PagerWrite(pPage1->pDbPage);
        if( rc==SQLITE_OK ){
          put4byte(&pPage1->aData[28], pBt->nPage);
        }
      }
    }
  }else if( rc==SQLITE_BUSY_SNAPSHOT && pBt->inTransaction==TRANS_NONE ){
    /* Even if there was no transaction opened when this function was
    ** called, a race condition may cause an SQLITE_BUSY_SNAPSHOT error
    ** in wal mode (since the code above opens a read-transaction and then
    ** upgrades it to a write-transaction - it does not take the write lock
    ** atomically). In this case change the error code to SQLITE_BUSY.  */
    assert( wrFlag );
    rc = SQLITE_BUSY;
  }


trans_begun:
  if( rc==SQLITE_OK ){
    if( pSchemaVersion ){
      *pSchemaVersion = get4byte(&pBt->pPage1->aData[40]);
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Changes to test/walprotocol2.test.
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  }
}
do_catchsql_test 2.2 {
  BEGIN EXCLUSIVE;
} {1 {database is locked}}
do_test 2.3 {
  sqlite3_extended_errcode db
} {SQLITE_BUSY_SNAPSHOT}
} {SQLITE_BUSY}

#---------------------------------------------------------------
# Same again, but with a busy-handler. This time, following the
# SQLITE_BUSY_SNAPSHOT error the busy-handler is invoked and then the 
# whole thing retried from the beginning. This time it succeeds.
#
proc lock_callback {method filename handle lock} {
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