Merge 'Make cursor seek reentrant' from Pedro Muniz

Closes #1628.  Every function that calls `process_overflow_read` needs
to be reentrant. I did not change it here, but it would include
`get_prev_record` and `get_next_record`. Maybe `tablebtree_move_to` did
not need to use the state machine, but I included it as a safeguard.
Edit: Closes #1625 . When I implemented `restore_context`, I forgot to
add a `return_if_io` after calling it in `next` 🤦‍♂️
Edit: Closes #1617 . Just tested it and it also solves this bug.

Reviewed-by: Jussi Saurio <jussi.saurio@gmail.com>

Closes #1636

core/vdbe/execute.rs

@@ -3907,6 +3907,7 @@ pub fn op_delete(
     Ok(InsnFunctionStepResult::Step)
 }
 
+#[derive(Debug)]
 pub enum OpIdxDeleteState {
     Seeking(ImmutableRecord), // First seek row to delete
     Deleting,

testing/cli_tests/memory.py

@@ -20,7 +20,10 @@ def stub_memory_test(
     # zero_blob_size = 1024 **2
     zero_blob = "0" * blob_size * 2
     # vals = 100
-    big_stmt = ["CREATE TABLE temp (t1 BLOB, t2 INTEGER);"]
+    big_stmt = [
+        "CREATE TABLE temp (t1 BLOB, t2 INTEGER);",
+        "CREATE INDEX temp_index ON temp(t1);",
+    ]
     big_stmt = big_stmt + [
         f"INSERT INTO temp (t1) VALUES (zeroblob({blob_size}));"
         if i % 2 == 0 and blobs
@@ -39,6 +42,10 @@ def stub_memory_test(
     big_stmt.append("SELECT count(*) FROM temp;")
     expected.append(str(vals * 2))
 
+    big_stmt.append("DELETE FROM temp;")
+    big_stmt.append("SELECT count(*) FROM temp;")
+    expected.append(str(0))
+
     big_stmt = "".join(big_stmt)
     expected = "\n".join(expected)
 

testing/cli_tests/write.py

@@ -19,7 +19,7 @@ class InsertTest(BaseModel):
 
     def run(self, limbo: TestLimboShell):
         zero_blob = "0" * self.blob_size * 2
-        big_stmt = [self.db_schema]
+        big_stmt = [self.db_schema, "CREATE INDEX test_index ON test(t1);"]
         big_stmt = big_stmt + [
             f"INSERT INTO test (t1) VALUES (zeroblob({self.blob_size}));"
             if i % 2 == 0 and self.has_blob
@@ -37,6 +37,10 @@ class InsertTest(BaseModel):
 
         big_stmt.append("SELECT count(*) FROM test;")
         expected.append(str(self.vals * 2))
+        
+        big_stmt.append("DELETE FROM temp;")
+        big_stmt.append("SELECT count(*) FROM temp;")
+        expected.append(str(0))
 
         big_stmt = "".join(big_stmt)
         expected = "\n".join(expected)

testing/update.test

@@ -163,3 +163,10 @@ do_execsql_test_on_specific_db {:memory:} update-true-expr {
 } {10|20|30
 10|20|30}
 
+# https://github.com/tursodatabase/limbo/issues/1625
+do_execsql_test_on_specific_db {:memory:} update_cache_full_regression_test_#1625 {
+    CREATE TABLE t(x);
+    INSERT INTO t VALUES (randomblob(4096));
+    UPDATE t SET x = randomblob(4096) WHERE rowid = 1;
+    SELECT count(*) FROM t;
+} {1}