// This function is invoked once for each page that has already been written into the log file when a WAL transaction is rolled back.
// Parameter iPg is the page number of said page. The pCtx argument is actually a pointer to the Pager structure.
//
// If page iPg is present in the cache, and has no outstanding references, it is discarded. Otherwise, if there are one or more outstanding
// references, the page content is reloaded from the database. If the attempt to reload content from the database is required and fails,
// return an SQLite error code. Otherwise, SQLITE.OK.
static int pagerUndoCallback(Pager pCtx, Pgno iPg)
{
var rc = SQLITE.OK;
Pager pPager = (Pager)pCtx;
PgHdr pPg;
pPg = sqlite3PagerLookup(pPager, iPg);
if (pPg)
{
if (sqlite3PcachePageRefcount(pPg) == 1)
{
sqlite3PcacheDrop(pPg);
}
else
{
rc = readDbPage(pPg);
if (rc == SQLITE.OK)
{
pPager.xReiniter(pPg);
}
sqlite3PagerUnref(pPg);
}
}
// Normally, if a transaction is rolled back, any backup processes are updated as data is copied out of the rollback journal and into the
// database. This is not generally possible with a WAL database, as rollback involves simply truncating the log file. Therefore, if one
// or more frames have already been written to the log (and therefore also copied into the backup databases) as part of this transaction,
// the backups must be restarted.
sqlite3BackupRestart(pPager.pBackup);
return(rc);
}
