Make the winTruncate() method of the windows VFS be a no-op if there are

outstanding references to the memory-mapped pages.  Otherwise, memory might
be deleted out from under those references when the file is remapped during
the truncate operation.

FossilOrigin-Name: ffce4aac18dacbf2a3112ae2ab56c7db20cb164f179683d90a66ef38f4a98f2b

diff --git a/manifest b/manifest
index 0d003ac9b5ad8e72f37c1a033856d30232a67b3a..07b7339969bbcf6a85174a9519ab204ee1c5cf75 100644 (file)
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Remove\sthe\sunused\smmapSizeActual\sfield\sfrom\sthe\sWindows\ssqlite3_file\nimplementation.
-D 2018-11-24T16:07:21.425
+C Make\sthe\swinTruncate()\smethod\sof\sthe\swindows\sVFS\sbe\sa\sno-op\sif\sthere\sare\noutstanding\sreferences\sto\sthe\smemory-mapped\spages.\s\sOtherwise,\smemory\smight\nbe\sdeleted\sout\sfrom\sunder\sthose\sreferences\swhen\sthe\sfile\sis\sremapped\sduring\nthe\struncate\soperation.
+D 2018-11-24T17:46:07.403
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F Makefile.in b730006b54c990461d864c5387f2e6f13aadb0236804555fb010ed6865a5f058
@@ -491,7 +491,7 @@ F src/os.h 48388821692e87da174ea198bf96b1b2d9d83be5dfc908f673ee21fafbe0d432
 F src/os_common.h b2f4707a603e36811d9b1a13278bffd757857b85
 F src/os_setup.h 0dbaea40a7d36bf311613d31342e0b99e2536586
 F src/os_unix.c f6e91b8fd82af7afbfd073c4974ad6cdb8e62d9f65ceddb45167835a0567fdc0
-F src/os_win.c fd94dd9c5738a65f629827df2df458fef8e827031ec99f7e2410bf5811ef979f
+F src/os_win.c 85d9e532d0444ab6c16d7431490c2e279e282aa0917b0e988996b1ae0de5c5a0
 F src/os_win.h 7b073010f1451abe501be30d12f6bc599824944a
 F src/pager.c ff1757f5bb5adb756f22e44c02b235e1d228c6d2c14ae4ea405f2eac7bb0f046
 F src/pager.h 1bffa1ba8a742f8b6485ace9fdbceb0924a15c589a0fb86338ce7ed75130b232
@@ -1004,7 +1004,7 @@ F test/incrblob4.test 21a52a6843a56cdcce968c6a86b72a7066d0e6ba
 F test/incrblob_err.test 89372a28f1d98254f03fed705f9efcd34ef61a674df16d2dbb4726944a2de5e9
 F test/incrblobfault.test 74dd8ac108304cea0b4a0df6df63a1567e558758
 F test/incrcorrupt.test 6c567fbf870aa9e91866fe52ce6f200cd548939a
-F test/incrvacuum.test b729aab1d4983037da57e66c20dfd7458561a85626dcf824f60175e35f4ce152
+F test/incrvacuum.test d67f6c8330587c6e96e34c19156b67b9f762cd302bdd1d89119fa6edea1ab49b
 F test/incrvacuum2.test 7d26cfda66c7e55898d196de54ac4ec7d86a4e3d
 F test/incrvacuum3.test 75256fb1377e7c39ef2de62bfc42bbff67be295a
 F test/incrvacuum_ioerr.test 6ae2f783424e47a0033304808fe27789cf93e635
@@ -1778,7 +1778,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 81629ba91475938b6ad528e7b1dbef4ad22239782bb2e9c1bb59413aba11da87
-R 4fb4a37d69ae99b1210a8898ab60ca45
+P 0e7aa62227d1d9c3540b54d7caf44a1ce7ccfa706672fc41dbb2be477ab3a667
+Q +8576ccb479fc4b76e950a5c2c5db5c57b59e3c17004b8cca478f0edafd386ec4
+R 9828e9d93ec79c8a535d23c9ae9db165
 U drh
-Z 28dc13c8bc7d6c615da3b9b59cc3c652
+Z 1144a278bdd73ccac6950d5ac3539f37

diff --git a/manifest.uuid b/manifest.uuid
index 46530511a0efcb2161537f596292f393b66d901c..5065af9a736deb5e493ba6106552c86994406d47 100644 (file)
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-0e7aa62227d1d9c3540b54d7caf44a1ce7ccfa706672fc41dbb2be477ab3a667
\ No newline at end of file
+ffce4aac18dacbf2a3112ae2ab56c7db20cb164f179683d90a66ef38f4a98f2b
\ No newline at end of file

diff --git a/src/os_win.c b/src/os_win.c
index 5eb7a9b38c767747c1399eccffeeab9caddccbc3..aafc89f7d2d5b912496dbdb2e0498c341cae75c5 100644 (file)
--- a/src/os_win.c
+++ b/src/os_win.c
@@ -2905,6 +2905,26 @@ static int winTruncate(sqlite3_file *id, sqlite3_int64 nByte){
   DWORD lastErrno;
 #if SQLITE_MAX_MMAP_SIZE>0
   sqlite3_int64 oldMmapSize;
+  if( pFile->nFetchOut>0 ){
+    /* File truncation is a no-op if there are outstanding memory mapped
+    ** pages.  This is because truncating the file means temporarily unmapping
+    ** the file, and that might delete memory out from under existing cursors.
+    **
+    ** This can result in incremental vacuum not truncating the file,
+    ** if there is an active read cursor when the incremental vacuum occurs.
+    ** No real harm comes of this - the database file is not corrupted,
+    ** though some folks might complain that the file is bigger than it
+    ** needs to be.
+    **
+    ** The only feasible work-around is to defer the truncation until after
+    ** all references to memory-mapped content are closed.  That is doable,
+    ** but involves adding a few branches in the common write code path which
+    ** could slow down normal operations slightly.  Hence, we have decided for
+    ** now to simply make trancations a no-op if there are pending reads.  We
+    ** can maybe revisit this decision in the future.
+    */
+    return SQLITE_OK;
+  }
 #endif
 
   assert( pFile );

diff --git a/test/incrvacuum.test b/test/incrvacuum.test
index 7004bbbcf4ad3a3b5135e07f3b5d3c05ab73ac10..d601fbf3147d9c83b760f5187b79c3c9d9485b06 100644 (file)
--- a/test/incrvacuum.test
+++ b/test/incrvacuum.test
@@ -783,4 +783,52 @@ do_test incrvacuum-15.1 {
   }
 } {ok}
 
+#-------------------------------------------------------------------------
+# At one point it was unsafe to truncate a db file on windows while there
+# were outstanding xFetch() references. This test case attempts to hit
+# that case.
+#
+reset_db
+do_execsql_test incrvacuum-16.0 {
+  PRAGMA auto_vacuum = 2;
+  CREATE TABLE t3(a);
+  INSERT INTO t3 VALUES(1), (2), (3), (4);
+
+  CREATE TABLE t2(x);
+  INSERT INTO t2 VALUES( randomblob(1000) );
+  INSERT INTO t2 VALUES( randomblob(1000) );
+  INSERT INTO t2 VALUES( randomblob(1000) );
+  INSERT INTO t2 VALUES( randomblob(1000) );
+  INSERT INTO t2 VALUES( randomblob(1000) );
+  INSERT INTO t2 VALUES( randomblob(1000) );
+} {}
+
+# Reopen db to ensure the page-cache is empty.
+#
+db close
+sqlite3 db test.db
+
+# Open db in mmap-mode. Open a transaction, delete some data, then run
+# incremental-vacuum. Do not commit the transaction. 
+#
+do_execsql_test incrvacuum-16.1 {
+  PRAGMA mmap_size = 1000000;
+  BEGIN;
+  DELETE FROM t2;
+  PRAGMA incremental_vacuum = 1000;
+} {1000000}
+
+# Scan through table t3 (which is all clean pages - so mmap is used). Then,
+# midway through, commit the transaction. This causes the db to be truncated
+# while there are outstanding xFetch pages.
+#
+do_test incrvacuum-16.2 {
+  set res [list]
+  db eval { SELECT a FROM t3 } {
+    if {$a==3} { db eval COMMIT }
+    lappend res $a
+  }
+  set res
+} {1 2 3 4}
+
 finish_test