Add a complex assert() that checks a pager invariant. (CVS 6934)

FossilOrigin-Name: 2e08ad7bf629485a79ccebcf4c413e9dcc0d3ccf

manifest

@@ -1,5 +1,5 @@
-C Add\sassert()\sstatements\sto\smore\stightly\sconstrain\sthe\sstate\sof\spager.c.\nRemove\sthe\sthree\spager*.test\sscripts\ssince\sthey\sviolate\sthe\sconstraints\nasserted\sabove\sby\smodifying\sthe\sstate\sof\sthe\ssystem\sin\sways\sthat\sit\scannot\nbe\smodified\sin\sa\slive\ssystem.\s(CVS\s6933)
-D 2009-07-25T04:12:02
+C Add\sa\scomplex\sassert()\sthat\schecks\sa\spager\sinvariant.\s(CVS\s6934)
+D 2009-07-25T11:40:08
 F Makefile.arm-wince-mingw32ce-gcc fcd5e9cd67fe88836360bb4f9ef4cb7f8e2fb5a0
 F Makefile.in df9359da7a726ccb67a45db905c5447d5c00c6ef
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -147,7 +147,7 @@ F src/os_common.h 8c61457df58f1a4bd5f5adc3e90e01b37bf7afbc
 F src/os_os2.c bed77dc26e3a95ce4a204936b9a1ca6fe612fcc5
 F src/os_unix.c cdb2a08b9ce4aa13b3f7b91d4dd60fb48be9f56a
 F src/os_win.c 725c38a524d168ce280446ad8761d731bc516405
-F src/pager.c e26d9c5d881435b83551a07cd7e38396518582bc
+F src/pager.c 2ccb1152741996d3f6125232f14dfcf654bdd29f
 F src/pager.h 11852d044c86cf5a9d6e34171fb0c4fcf1f6265f
 F src/parse.y bcd46d43fbd23a22b8c020a3eb1806b794794ed5
 F src/pcache.c 1dae135b70a029f81ed66f6e9b5d0db91480d5d0
@@ -738,7 +738,7 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl 672f81d693a03f80f5ae60bfefacd8a349e76746
-P 788aa9dde9e76f67f22c07a904faf03e97e032c6
-R 4116dfd49c9a3af1d9a66719263f82dc
-U drh
-Z 51e179b626e42eaf6ce7a289270b3c19
+P 3b6d370ed68eaf9636b26c7240a8b3a43d2edd70
+R 6427dd1fa4bac8adebaeed3a85e8f4b9
+U danielk1977
+Z ea5eb9c594b637c9c13eaf08f55c7f0a

manifest.uuid

@@ -1 +1 @@
-3b6d370ed68eaf9636b26c7240a8b3a43d2edd70
+2e08ad7bf629485a79ccebcf4c413e9dcc0d3ccf

src/pager.c

@@ -18,7 +18,7 @@
 ** file simultaneously, or one process from reading the database while
 ** another is writing.
 **
-** @(#) $Id: pager.c,v 1.620 2009/07/25 04:12:02 drh Exp $
+** @(#) $Id: pager.c,v 1.621 2009/07/25 11:40:08 danielk1977 Exp $
 */
 #ifndef SQLITE_OMIT_DISKIO
 #include "sqliteInt.h"
@@ -2625,6 +2625,40 @@ static int pager_wait_on_lock(Pager *pPager, int locktype){
   return rc;
 }
 
+/*
+** Function assertTruncateConstraint(pPager) checks that one of the 
+** following is true for all dirty pages currently in the page-cache:
+**
+**   a) The page number is less than or equal to the size of the 
+**      current database image, in pages, OR
+**
+**   b) if the page content were written at this time, it would not
+**      be necessary to write the current content out to the sub-journal
+**      (as determined by function subjRequiresPage()).
+**
+** If the condition asserted by this function were not true, and the
+** dirty page were to be discarded from the cache via the pagerStress()
+** routine, pagerStress() would not write the current page content to
+** the database file. If a savepoint transaction were rolled back after
+** this happened, the correct behaviour would be to restore the current
+** content of the page. However, since this content is not present in either
+** the database file or the portion of the rollback journal and 
+** sub-journal rolled back the content could not be restored and the
+** database image would become corrupt. It is therefore fortunate that 
+** this circumstance cannot arise.
+*/
+#if defined(SQLITE_DEBUG)
+static void assertTruncateConstraintCb(PgHdr *pPg){
+  assert( pPg->flags&PGHDR_DIRTY );
+  assert( !subjRequiresPage(pPg) || pPg->pgno<=pPg->pPager->dbSize );
+}
+static void assertTruncateConstraint(Pager *pPager){
+  sqlite3PcacheIterateDirty(pPager->pPCache, assertTruncateConstraintCb);
+}
+#else
+# define assertTruncateConstraint(pPager)
+#endif
+
 /*
 ** Truncate the in-memory database file image to nPage pages. This 
 ** function does not actually modify the database file on disk. It 
@@ -2636,6 +2670,7 @@ void sqlite3PagerTruncateImage(Pager *pPager, Pgno nPage){
   assert( pPager->dbSize>=nPage );
   assert( pPager->state>=PAGER_RESERVED );
   pPager->dbSize = nPage;
+  assertTruncateConstraint(pPager);
 }
 
 /*
@@ -4963,6 +4998,7 @@ int sqlite3PagerOpenSavepoint(Pager *pPager, int nSavepoint){
 
     /* Open the sub-journal, if it is not already opened. */
     rc = openSubJournal(pPager);
+    assertTruncateConstraint(pPager);
   }
 
   return rc;