Add the SQLITE_FCNTL_RESET_CACHE verb. Use it to ensure that the page cache is purged before and after a the recovery extension is run.

FossilOrigin-Name: 6db0bc4bc0d272b610bef2aeeae43f539ed6e7cc0a9cc767d5af85ecb0019d5f

4 files changed, 23 insertions, 0 deletions

diff --git a/src/btree.c b/src/btree.c
index cabcf675e..c949001b8 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -11083,6 +11083,17 @@ int sqlite3BtreeIsReadonly(Btree *p){
 */
 int sqlite3HeaderSizeBtree(void){ return ROUND8(sizeof(MemPage)); }
 
+/*
+** If no transaction is active and the database is not a temp-db, clear
+** the in-memory pager cache.
+*/
+void sqlite3BtreeClearCache(Btree *p){
+  BtShared *pBt = p->pBt;
+  if( pBt->inTransaction==TRANS_NONE ){
+    sqlite3PagerClearCache(pBt->pPager);
+  }
+}
+
 #if !defined(SQLITE_OMIT_SHARED_CACHE)
 /*
 ** Return true if the Btree passed as the only argument is sharable.
diff --git a/src/btree.h b/src/btree.h
index 7f31c6020..c9b9d8017 100644
--- a/src/btree.h
+++ b/src/btree.h
@@ -368,6 +368,8 @@ void sqlite3BtreeCursorList(Btree*);
 
 int sqlite3BtreeTransferRow(BtCursor*, BtCursor*, i64);
 
+void sqlite3BtreeClearCache(Btree*);
+
 /*
 ** If we are not using shared cache, then there is no need to
 ** use mutexes to access the BtShared structures.  So make the
diff --git a/src/main.c b/src/main.c
index b0645efe6..67dd60ae7 100644
--- a/src/main.c
+++ b/src/main.c
@@ -3950,6 +3950,9 @@ int sqlite3_file_control(sqlite3 *db, const char *zDbName, int op, void *pArg){
         sqlite3BtreeSetPageSize(pBtree, 0, iNew, 0);
       }
       rc = SQLITE_OK;
+    }else if( op==SQLITE_FCNTL_RESET_CACHE ){
+      sqlite3BtreeClearCache(pBtree);
+      rc = SQLITE_OK;
     }else{
       int nSave = db->busyHandler.nBusy;
       rc = sqlite3OsFileControl(fd, op, pArg);
diff --git a/src/sqlite.h.in b/src/sqlite.h.in
index c2fc4e5a6..369d6b602 100644
--- a/src/sqlite.h.in
+++ b/src/sqlite.h.in
@@ -1192,6 +1192,12 @@ struct sqlite3_io_methods {
 **
 ** <li>[[SQLITE_FCNTL_CKSM_FILE]]
 ** Used by the cksmvfs VFS module only.
+**
+** <li>[[SQLITE_FCNTL_RESET_CACHE]]
+** If there is currently no transaction open on the database, and the 
+** database is not a temp db, then this file-control purges the contents
+** of the in-memory page cache. If there is an open transaction, or if
+** the db is a temp-db, it is a no-op, not an error.
 ** </ul>
 */
 #define SQLITE_FCNTL_LOCKSTATE               1
@@ -1234,6 +1240,7 @@ struct sqlite3_io_methods {
 #define SQLITE_FCNTL_CKPT_START             39
 #define SQLITE_FCNTL_EXTERNAL_READER        40
 #define SQLITE_FCNTL_CKSM_FILE              41
+#define SQLITE_FCNTL_RESET_CACHE            42
 
 /* deprecated names */
 #define SQLITE_GET_LOCKPROXYFILE      SQLITE_FCNTL_GET_LOCKPROXYFILE