Allow sqlite3_snapshot_open() to be called to change the snapshot after a

read transaction is already open on database.

FossilOrigin-Name: 051ac0152048ef52723196c26ca5f2629dafb782aec1c66fc30531bf54335043

1 files changed, 21 insertions, 3 deletions

diff --git a/src/main.c b/src/main.c
index 4ae5c7ecd..4ea7c2077 100644
--- a/src/main.c
+++ b/src/main.c
@@ -4209,11 +4209,29 @@ int sqlite3_snapshot_open(
     iDb = sqlite3FindDbName(db, zDb);
     if( iDb==0 || iDb>1 ){
       Btree *pBt = db->aDb[iDb].pBt;
-      if( 0==sqlite3BtreeIsInReadTrans(pBt) ){
-        rc = sqlite3PagerSnapshotOpen(sqlite3BtreePager(pBt), pSnapshot);
+      if( sqlite3BtreeIsInTrans(pBt)==0 ){
+        Pager *pPager = sqlite3BtreePager(pBt);
+        int bUnlock = 0;
+        if( sqlite3BtreeIsInReadTrans(pBt) ){
+          if( db->nVdbeActive==0 ){
+            rc = sqlite3PagerSnapshotCheck(pPager, pSnapshot);
+            if( rc==SQLITE_OK ){
+              bUnlock = 1;
+              rc = sqlite3BtreeCommit(pBt);
+            }
+          }
+        }else{
+          rc = SQLITE_OK;
+        }
+        if( rc==SQLITE_OK ){
+          rc = sqlite3PagerSnapshotOpen(pPager, pSnapshot);
+        }
         if( rc==SQLITE_OK ){
           rc = sqlite3BtreeBeginTrans(pBt, 0, 0);
-          sqlite3PagerSnapshotOpen(sqlite3BtreePager(pBt), 0);
+          sqlite3PagerSnapshotOpen(pPager, 0);
+        }
+        if( bUnlock ){
+          sqlite3PagerSnapshotUnlock(pPager);
         }
       }
     }