Index: src/btree.c
===================================================================
--- src/btree.c	2009-09-09 06:45:19.000000000 -0700
+++ src/btree.c	2009-09-14 18:17:53.000000000 -0700
@@ -24,6 +24,12 @@
 static const char zMagicHeader[] = SQLITE_FILE_HEADER;
 
 /*
+** The header string that appears at the beginning of a SQLite
+** database which has been poisoned.
+*/
+static const char zPoisonHeader[] = "SQLite poison 3";
+
+/*
 ** Set this global variable to 1 to enable tracing using the TRACE
 ** macro.
 */
@@ -2337,6 +2343,7 @@
   if( rc ) return rc;
   memcpy(data, zMagicHeader, sizeof(zMagicHeader));
   assert( sizeof(zMagicHeader)==16 );
+  assert( sizeof(zMagicHeader)==sizeof(zPoisonHeader) );
   put2byte(&data[16], pBt->pageSize);
   data[18] = 1;
   data[19] = 1;
@@ -7804,4 +7811,72 @@
   assert(!pCur->aOverflow);
   pCur->isIncrblobHandle = 1;
 }
+
+/* Poison the db so that other clients error out as quickly as
+** possible.
+*/
+int sqlite3Poison(sqlite3 *db){
+  int rc;
+  Btree *p;
+  BtShared *pBt;
+  unsigned char *pP1;
+
+  if( db == NULL) return SQLITE_OK;
+
+  /* Database 0 corrosponds to the main database. */
+  if( db->nDb<1 ) return SQLITE_OK;
+  p = db->aDb[0].pBt;
+  pBt = p->pBt;
+
+  /* If in a transaction, roll it back.  Committing any changes to a
+  ** corrupt database may mess up evidence, we definitely don't want
+  ** to allow poisoning to be rolled back, and the database is anyhow
+  ** going bye-bye RSN.
+  */
+  /* TODO(shess): Figure out if this might release the lock and let
+  ** someone else get in there, which might deny us the lock a couple
+  ** lines down.
+  */
+  if( sqlite3BtreeIsInTrans(p) ) sqlite3BtreeRollback(p);
+
+  /* Start an exclusive transaction.  This will check the headers, so
+  ** if someone else poisoned the database we should get an error.
+  */
+  rc = sqlite3BtreeBeginTrans(p, 2);
+  /* TODO(shess): Handle SQLITE_BUSY? */
+  if( rc!=SQLITE_OK ) return rc;
+
+  /* Copied from sqlite3BtreeUpdateMeta().  Writing the old version of
+  ** the page to the journal may be overkill, but it probably won't
+  ** hurt.
+  */
+  assert( pBt->inTrans==TRANS_WRITE );
+  assert( pBt->pPage1!=0 );
+  rc = sqlite3PagerWrite(pBt->pPage1->pDbPage);
+  if( rc ) goto err;
+
+  /* "SQLite format 3" changes to
+  ** "SQLite poison 3".  Be extra paranoid about making this change.
+  */
+  if( sizeof(zMagicHeader)!=16 ||
+      sizeof(zPoisonHeader)!=sizeof(zMagicHeader) ){
+    rc = SQLITE_ERROR;
+    goto err;
+  }
+  pP1 = pBt->pPage1->aData;
+  if( memcmp(pP1, zMagicHeader, 16)!=0 ){
+    rc = SQLITE_CORRUPT;
+    goto err;
+  }
+  memcpy(pP1, zPoisonHeader, 16);
+
+  /* Push it to the database file. */
+  return sqlite3BtreeCommit(p);
+
+ err:
+  /* TODO(shess): What about errors, here? */
+  sqlite3BtreeRollback(p);
+  return rc;
+}
+
 #endif