For an existing multiplexed database, try to set the chunk size automatically

based on the sizes of the preexisting pieces.

FossilOrigin-Name: 427a9a5120a68bfa12fec97cfd02eb9b28b3fa6b

manifest

@@ -1,5 +1,5 @@
-C All\sthe\sSQLITE_OPEN_URI\sflag\sto\spropagate\sdown\sinto\sthe\sVFS.
-D 2011-07-20T17:13:30.035
+C For\san\sexisting\smultiplexed\sdatabase,\stry\sto\sset\sthe\schunk\ssize\sautomatically\nbased\son\sthe\ssizes\sof\sthe\spreexisting\spieces.
+D 2011-07-20T17:59:38.568
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in c1d7a7f4fd8da6b1815032efca950e3d5125407e
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -213,7 +213,7 @@ F src/test_intarray.h 489edb9068bb926583445cb02589344961054207
 F src/test_journal.c 03313c693cca72959dcaaf79f8d76f21c01e19ff
 F src/test_loadext.c df586c27176e3c2cb2e099c78da67bf14379a56e
 F src/test_malloc.c 7ca7be34e0e09ef0ed6619544552ed95732e41f6
-F src/test_multiplex.c 282f315fd035c8d8342a4cc59748c60216b61fef
+F src/test_multiplex.c 7f5b2ec63ff514f12e95ffbe134fca87eaac7e96
 F src/test_multiplex.h e99c571bc4968b7a9363b661481f3934bfead61d
 F src/test_mutex.c a6bd7b9cf6e19d989e31392b06ac8d189f0d573e
 F src/test_onefile.c 40cf9e212a377a6511469384a64b01e6e34b2eec
@@ -952,7 +952,7 @@ F tool/symbols.sh caaf6ccc7300fd43353318b44524853e222557d5
 F tool/tostr.awk 11760e1b94a5d3dcd42378f3cc18544c06cfa576
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
 F tool/warnings.sh 2ebae31e1eb352696f3c2f7706a34c084b28c262
-P 1ffa542bf913200a18ef77447aec4fc3ca1ed618
-R a8712e3b34abd0caa57ff420866bce41
+P 29866f9598502a007816410fade34f1d0952dea0
+R f7447480ebd05c67794755dbb19b5608
 U drh
-Z aa653174b90521d7bcecad6884ea5241
+Z ce5790e6bda5ced4f7371ad338df0dcd

manifest.uuid

@@ -1 +1 @@
-29866f9598502a007816410fade34f1d0952dea0
+427a9a5120a68bfa12fec97cfd02eb9b28b3fa6b

src/test_multiplex.c

@@ -453,7 +453,7 @@ static int multiplexOpen(
   int rc = SQLITE_OK;                  /* Result code */
   multiplexConn *pMultiplexOpen;       /* The new multiplex file descriptor */
   multiplexGroup *pGroup;              /* Corresponding multiplexGroup object */
-  sqlite3_file *pSubOpen;                        /* Real file descriptor */
+  sqlite3_file *pSubOpen = 0;                    /* Real file descriptor */
   sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;   /* Real VFS */
   int nName;
   int sz;
@@ -513,16 +513,35 @@ static int multiplexOpen(
     memcpy(pGroup->zName, zName, nName+1);
     pGroup->nName = nName;
     pGroup->flags = flags;
-    pSubOpen = multiplexSubOpen(pGroup, 0, &rc, pOutFlags);
+    rc = multiplexSubFilename(pGroup, 1);
+    if( rc==SQLITE_OK ){
+      pSubOpen = multiplexSubOpen(pGroup, 0, &rc, pOutFlags);
+    }
     if( pSubOpen ){
-      /* if this file is already larger than chunk size, disable 
-      ** the multiplex feature.
-      */
+      int exists, rc2, rc3;
       sqlite3_int64 sz;
-      int rc2 = pSubOpen->pMethods->xFileSize(pSubOpen, &sz);
-      if( (rc2==SQLITE_OK) && (sz>pGroup->nChunkSize) ){
-        pGroup->bEnabled = 0;
+
+      rc2 = pSubOpen->pMethods->xFileSize(pSubOpen, &sz);
+      if( rc2==SQLITE_OK ){
+        /* If the first overflow file exists and if the size of the main file
+        ** is different from the chunk size, that means the chunk size is set
+        ** set incorrectly.  So fix it.
+        **
+        ** Or, if the first overflow file does not exist and the main file is
+        ** larger than the chunk size, that means the chunk size is too small.
+        ** But we have no way of determining the intended chunk size, so 
+        ** just disable the multiplexor all togethre.
+        */
+        rc3 = pOrigVfs->xAccess(pOrigVfs, pGroup->aReal[1].z,
+            SQLITE_ACCESS_EXISTS, &exists);
+        if( rc3==SQLITE_OK && exists && sz==(sz&0xffff0000) && sz>0
+            && sz!=pGroup->nChunkSize ){
+          pGroup->nChunkSize = sz;
+        }else if( rc3==SQLITE_OK && !exists && sz>pGroup->nChunkSize ){
+          pGroup->bEnabled = 0;
+        }
       }
+
       if( pSubOpen->pMethods->iVersion==1 ){
         pMultiplexOpen->base.pMethods = &gMultiplex.sIoMethodsV1;
       }else{
@@ -780,10 +799,10 @@ static int multiplexFileSize(sqlite3_file *pConn, sqlite3_int64 *pSize){
       rc = pSubOpen->pMethods->xFileSize(pSubOpen, pSize);
     }
   }else{
+    sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;
     *pSize = 0;
     for(i=0; 1; i++){
       sqlite3_file *pSubOpen = 0;
-      sqlite3_vfs *pOrigVfs = gMultiplex.pOrigVfs;
       int exists = 0;
       rc = multiplexSubFilename(pGroup, i);
       if( rc ) break;