Index: src/os_unix.c
==================================================================
--- src/os_unix.c
+++ src/os_unix.c
@@ -208,11 +208,11 @@
   int h;                              /* The file descriptor */
   unsigned char eFileLock;            /* The type of lock held on this fd */
   unsigned short int ctrlFlags;       /* Behavioral bits.  UNIXFILE_* flags */
   int lastErrno;                      /* The unix errno from last I/O error */
   void *lockingContext;               /* Locking style specific state */
-  UnixUnusedFd *pUnused;              /* Pre-allocated UnixUnusedFd */
+  UnixUnusedFd *pPreallocatedUnused;  /* Pre-allocated UnixUnusedFd */
   const char *zPath;                  /* Name of the file */
   unixShm *pShm;                      /* Shared memory segment information */
   int szChunk;                        /* Configured by FCNTL_CHUNK_SIZE */
 #if SQLITE_MAX_MMAP_SIZE>0
   int nFetchOut;                      /* Number of outstanding xFetch refs */
@@ -1118,11 +1118,12 @@
 };
 
 /*
 ** A lists of all unixInodeInfo objects.
 */
-static unixInodeInfo *inodeList = 0;
+static unixInodeInfo *inodeList = 0;  /* All unixInodeInfo objects */
+static unsigned int nUnusedFd = 0;    /* Total unused file descriptors */
 
 /*
 **
 ** This function - unixLogErrorAtLine(), is only ever called via the macro
 ** unixLogError().
@@ -1228,10 +1229,11 @@
   UnixUnusedFd *pNext;
   for(p=pInode->pUnused; p; p=pNext){
     pNext = p->pNext;
     robust_close(pFile, p->fd, __LINE__);
     sqlite3_free(p);
+    nUnusedFd--;
   }
   pInode->pUnused = 0;
 }
 
 /*
@@ -1260,10 +1262,11 @@
         pInode->pNext->pPrev = pInode->pPrev;
       }
       sqlite3_free(pInode);
     }
   }
+  assert( inodeList!=0 || nUnusedFd==0 );
 }
 
 /*
 ** Given a file descriptor, locate the unixInodeInfo object that
 ** describes that file descriptor.  Create a new one if necessary.  The
@@ -1329,10 +1332,11 @@
 #if OS_VXWORKS
   fileId.pId = pFile->pId;
 #else
   fileId.ino = (u64)statbuf.st_ino;
 #endif
+  assert( inodeList!=0 || nUnusedFd==0 );
   pInode = inodeList;
   while( pInode && memcmp(&fileId, &pInode->fileId, sizeof(fileId)) ){
     pInode = pInode->pNext;
   }
   if( pInode==0 ){
@@ -1748,15 +1752,16 @@
 ** Add the file descriptor used by file handle pFile to the corresponding
 ** pUnused list.
 */
 static void setPendingFd(unixFile *pFile){
   unixInodeInfo *pInode = pFile->pInode;
-  UnixUnusedFd *p = pFile->pUnused;
+  UnixUnusedFd *p = pFile->pPreallocatedUnused;
   p->pNext = pInode->pUnused;
   pInode->pUnused = p;
   pFile->h = -1;
-  pFile->pUnused = 0;
+  pFile->pPreallocatedUnused = 0;
+  nUnusedFd++;
 }
 
 /*
 ** Lower the locking level on file descriptor pFile to eFileLock.  eFileLock
 ** must be either NO_LOCK or SHARED_LOCK.
@@ -1977,11 +1982,11 @@
     pFile->zPath = 0;
   }
 #endif
   OSTRACE(("CLOSE   %-3d\n", pFile->h));
   OpenCounter(-1);
-  sqlite3_free(pFile->pUnused);
+  sqlite3_free(pFile->pPreallocatedUnused);
   memset(pFile, 0, sizeof(unixFile));
   return SQLITE_OK;
 }
 
 /*
@@ -3198,11 +3203,11 @@
   assert( amt>0 );
 
   /* If this is a database file (not a journal, master-journal or temp
   ** file), the bytes in the locking range should never be read or written. */
 #if 0
-  assert( pFile->pUnused==0
+  assert( pFile->pPreallocatedUnused==0
        || offset>=PENDING_BYTE+512
        || offset+amt<=PENDING_BYTE 
   );
 #endif
 
@@ -3311,11 +3316,11 @@
   assert( amt>0 );
 
   /* If this is a database file (not a journal, master-journal or temp
   ** file), the bytes in the locking range should never be read or written. */
 #if 0
-  assert( pFile->pUnused==0
+  assert( pFile->pPreallocatedUnused==0
        || offset>=PENDING_BYTE+512
        || offset+amt<=PENDING_BYTE 
   );
 #endif
 
@@ -5561,23 +5566,24 @@
   ** but because no way to test it is currently available. It is better 
   ** not to risk breaking vxworks support for the sake of such an obscure 
   ** feature.  */
 #if !OS_VXWORKS
   struct stat sStat;                   /* Results of stat() call */
+
+  unixEnterMutex();
 
   /* A stat() call may fail for various reasons. If this happens, it is
   ** almost certain that an open() call on the same path will also fail.
   ** For this reason, if an error occurs in the stat() call here, it is
   ** ignored and -1 is returned. The caller will try to open a new file
   ** descriptor on the same path, fail, and return an error to SQLite.
   **
   ** Even if a subsequent open() call does succeed, the consequences of
   ** not searching for a reusable file descriptor are not dire.  */
-  if( 0==osStat(zPath, &sStat) ){
+  if( nUnusedFd>0 && 0==osStat(zPath, &sStat) ){
     unixInodeInfo *pInode;
 
-    unixEnterMutex();
     pInode = inodeList;
     while( pInode && (pInode->fileId.dev!=sStat.st_dev
                      || pInode->fileId.ino!=(u64)sStat.st_ino) ){
        pInode = pInode->pNext;
     }
@@ -5584,15 +5590,16 @@
     if( pInode ){
       UnixUnusedFd **pp;
       for(pp=&pInode->pUnused; *pp && (*pp)->flags!=flags; pp=&((*pp)->pNext));
       pUnused = *pp;
       if( pUnused ){
+        nUnusedFd--;
         *pp = pUnused->pNext;
       }
     }
-    unixLeaveMutex();
   }
+  unixLeaveMutex();
 #endif    /* if !OS_VXWORKS */
   return pUnused;
 }
 
 /*
@@ -5809,11 +5816,11 @@
       pUnused = sqlite3_malloc64(sizeof(*pUnused));
       if( !pUnused ){
         return SQLITE_NOMEM_BKPT;
       }
     }
-    p->pUnused = pUnused;
+    p->pPreallocatedUnused = pUnused;
 
     /* Database filenames are double-zero terminated if they are not
     ** URIs with parameters.  Hence, they can always be passed into
     ** sqlite3_uri_parameter(). */
     assert( (flags & SQLITE_OPEN_URI) || zName[strlen(zName)+1]==0 );
@@ -5846,11 +5853,11 @@
     mode_t openMode;              /* Permissions to create file with */
     uid_t uid;                    /* Userid for the file */
     gid_t gid;                    /* Groupid for the file */
     rc = findCreateFileMode(zName, flags, &openMode, &uid, &gid);
     if( rc!=SQLITE_OK ){
-      assert( !p->pUnused );
+      assert( !p->pPreallocatedUnused );
       assert( eType==SQLITE_OPEN_WAL || eType==SQLITE_OPEN_MAIN_JOURNAL );
       return rc;
     }
     fd = robust_open(zName, openFlags, openMode);
     OSTRACE(("OPENX   %-3d %s 0%o\n", fd, zName, openFlags));
@@ -5880,13 +5887,13 @@
   assert( fd>=0 );
   if( pOutFlags ){
     *pOutFlags = flags;
   }
 
-  if( p->pUnused ){
-    p->pUnused->fd = fd;
-    p->pUnused->flags = flags;
+  if( p->pPreallocatedUnused ){
+    p->pPreallocatedUnused->fd = fd;
+    p->pPreallocatedUnused->flags = flags;
   }
 
   if( isDelete ){
 #if OS_VXWORKS
     zPath = zName;
@@ -5963,11 +5970,11 @@
   
   rc = fillInUnixFile(pVfs, fd, pFile, zPath, ctrlFlags);
 
 open_finished:
   if( rc!=SQLITE_OK ){
-    sqlite3_free(p->pUnused);
+    sqlite3_free(p->pPreallocatedUnused);
   }
   return rc;
 }
 
 
@@ -6704,11 +6711,11 @@
   memset(&dummyVfs, 0, sizeof(dummyVfs));
   dummyVfs.pAppData = (void*)&autolockIoFinder;
   dummyVfs.zName = "dummy";
   pUnused->fd = fd;
   pUnused->flags = openFlags;
-  pNew->pUnused = pUnused;
+  pNew->pPreallocatedUnused = pUnused;
   
   rc = fillInUnixFile(&dummyVfs, fd, (sqlite3_file*)pNew, path, 0);
   if( rc==SQLITE_OK ){
     *ppFile = pNew;
     return SQLITE_OK;