turso/core/vdbe/mod.rs

//! The virtual database engine (VDBE).
//!
//! The VDBE is a register-based virtual machine that execute bytecode
//! instructions that represent SQL statements. When an application prepares
//! an SQL statement, the statement is compiled into a sequence of bytecode
//! instructions that perform the needed operations, such as reading or
//! writing to a b-tree, sorting, or aggregating data.
//!
//! The instruction set of the VDBE is similar to SQLite's instruction set,
//! but with the exception that bytecodes that perform I/O operations are
//! return execution back to the caller instead of blocking. This is because
//! Turso is designed for applications that need high concurrency such as
//! serverless runtimes. In addition, asynchronous I/O makes storage
//! disaggregation easier.
//!
//! You can find a full list of SQLite opcodes at:
//!
//! https://www.sqlite.org/opcode.html

pub mod builder;
pub mod execute;
pub mod explain;
pub mod insn;
pub mod likeop;
pub mod sorter;

use crate::{
    error::LimboError,
    function::{AggFunc, FuncCtx},
    state_machine::StateTransition,
    storage::sqlite3_ondisk::SmallVec,
    translate::collate::CollationSeq,
    translate::plan::TableReferences,
    types::{IOResult, RawSlice, TextRef},
    vdbe::execute::{
        OpIdxInsertState, OpInsertState, OpNewRowidState, OpNoConflictState, OpSeekState,
    },
    RefValue,
};

use crate::{
    storage::pager::Pager,
    translate::plan::ResultSetColumn,
    types::{AggContext, Cursor, ImmutableRecord, Value},
    vdbe::{builder::CursorType, insn::Insn},
};

#[cfg(feature = "json")]
use crate::json::JsonCacheCell;
use crate::{Connection, MvStore, Result, TransactionState};
use builder::CursorKey;
use execute::{
    InsnFunction, InsnFunctionStepResult, OpIdxDeleteState, OpIntegrityCheckState,
    OpOpenEphemeralState,
};

use regex::Regex;
use std::{
    cell::{Cell, RefCell},
    collections::HashMap,
    num::NonZero,
    rc::Rc,
    sync::Arc,
};
use tracing::{instrument, Level};

/// We use labels to indicate that we want to jump to whatever the instruction offset
/// will be at runtime, because the offset cannot always be determined when the jump
/// instruction is created.
///
/// In some cases, we want to jump to EXACTLY a specific instruction.
/// - Example: a condition is not met, so we want to jump to wherever Halt is.
///
/// In other cases, we don't care what the exact instruction is, but we know that we
/// want to jump to whatever comes AFTER a certain instruction.
/// - Example: a Next instruction will want to jump to "whatever the start of the loop is",
///   but it doesn't care what instruction that is.
///
/// The reason this distinction is important is that we might reorder instructions that are
/// constant at compile time, and when we do that, we need to change the offsets of any impacted
/// jump instructions, so the instruction that comes immediately after "next Insn" might have changed during the reordering.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum JumpTarget {
    ExactlyThisInsn,
    AfterThisInsn,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
/// Represents a target for a jump instruction.
/// Stores 32-bit ints to keep the enum word-sized.
pub enum BranchOffset {
    /// A label is a named location in the program.
    /// If there are references to it, it must always be resolved to an Offset
    /// via program.resolve_label().
    Label(u32),
    /// An offset is a direct index into the instruction list.
    Offset(InsnReference),
    /// A placeholder is a temporary value to satisfy the compiler.
    /// It must be set later.
    Placeholder,
}

impl BranchOffset {
    /// Returns true if the branch offset is a label.
    pub fn is_label(&self) -> bool {
        matches!(self, BranchOffset::Label(_))
    }

    /// Returns true if the branch offset is an offset.
    pub fn is_offset(&self) -> bool {
        matches!(self, BranchOffset::Offset(_))
    }

    /// Returns the offset value. Panics if the branch offset is a label or placeholder.
    pub fn as_offset_int(&self) -> InsnReference {
        match self {
            BranchOffset::Label(v) => unreachable!("Unresolved label: {}", v),
            BranchOffset::Offset(v) => *v,
            BranchOffset::Placeholder => unreachable!("Unresolved placeholder"),
        }
    }

    /// Returns the branch offset as a signed integer.
    /// Used in explain output, where we don't want to panic in case we have an unresolved
    /// label or placeholder.
    pub fn as_debug_int(&self) -> i32 {
        match self {
            BranchOffset::Label(v) => *v as i32,
            BranchOffset::Offset(v) => *v as i32,
            BranchOffset::Placeholder => i32::MAX,
        }
    }

    /// Adds an integer value to the branch offset.
    /// Returns a new branch offset.
    /// Panics if the branch offset is a label or placeholder.
    pub fn add<N: Into<u32>>(self, n: N) -> BranchOffset {
        BranchOffset::Offset(self.as_offset_int() + n.into())
    }

    pub fn sub<N: Into<u32>>(self, n: N) -> BranchOffset {
        BranchOffset::Offset(self.as_offset_int() - n.into())
    }
}

pub type CursorID = usize;

pub type PageIdx = usize;

// Index of insn in list of insns
type InsnReference = u32;

#[derive(Debug)]
pub enum StepResult {
    Done,
    IO,
    Row,
    Interrupt,
    Busy,
}

/// If there is I/O, the instruction is restarted.
/// Evaluate a Result<IOResult<T>>, if IO return Ok(StepResult::IO).
#[macro_export]
macro_rules! return_step_if_io {
    ($expr:expr) => {
        match $expr? {
            IOResult::Ok(v) => v,
            IOResult::IO => return Ok(StepResult::IO),
        }
    };
}

struct RegexCache {
    like: HashMap<String, Regex>,
    glob: HashMap<String, Regex>,
}

impl RegexCache {
    fn new() -> Self {
        Self {
            like: HashMap::new(),
            glob: HashMap::new(),
        }
    }
}

struct Bitfield<const N: usize>([u64; N]);

impl<const N: usize> Bitfield<N> {
    fn new() -> Self {
        Self([0; N])
    }

    fn set(&mut self, bit: usize) {
        assert!(bit < N * 64, "bit out of bounds");
        self.0[bit / 64] |= 1 << (bit % 64);
    }

    fn unset(&mut self, bit: usize) {
        assert!(bit < N * 64, "bit out of bounds");
        self.0[bit / 64] &= !(1 << (bit % 64));
    }

    fn get(&self, bit: usize) -> bool {
        assert!(bit < N * 64, "bit out of bounds");
        (self.0[bit / 64] & (1 << (bit % 64))) != 0
    }
}

#[derive(Debug, Copy, Clone, PartialEq, Eq)]
/// The commit state of the program.
/// There are two states:
/// - Ready: The program is ready to run the next instruction, or has shut down after
///   the last instruction.
/// - Committing: The program is committing a write transaction. It is waiting for the pager to finish flushing the cache to disk,
///   primarily to the WAL, but also possibly checkpointing the WAL to the database file.
enum CommitState {
    Ready,
    Committing,
}

#[derive(Debug, Clone)]
pub enum Register {
    Value(Value),
    Aggregate(AggContext),
    Record(ImmutableRecord),
}

/// A row is a the list of registers that hold the values for a filtered row. This row is a pointer, therefore
/// after stepping again, row will be invalidated to be sure it doesn't point to somewhere unexpected.
#[derive(Debug)]
pub struct Row {
    values: *const Register,
    count: usize,
}

/// The program state describes the environment in which the program executes.
pub struct ProgramState {
    pub pc: InsnReference,
    cursors: RefCell<Vec<Option<Cursor>>>,
    registers: Vec<Register>,
    pub(crate) result_row: Option<Row>,
    last_compare: Option<std::cmp::Ordering>,
    deferred_seeks: Vec<Option<(CursorID, CursorID)>>,
    ended_coroutine: Bitfield<4>, // flag to indicate that a coroutine has ended (key is the yield register. currently we assume that the yield register is always between 0-255, YOLO)
    /// Indicate whether an [Insn::Once] instruction at a given program counter position has already been executed, well, once.
    once: SmallVec<u32, 4>,
    regex_cache: RegexCache,
    pub(crate) mv_tx_id: Option<crate::mvcc::database::TxID>,
    interrupted: bool,
    pub parameters: HashMap<NonZero<usize>, Value>,
    commit_state: CommitState,
    #[cfg(feature = "json")]
    json_cache: JsonCacheCell,
    op_idx_delete_state: Option<OpIdxDeleteState>,
    op_integrity_check_state: OpIntegrityCheckState,
    op_open_ephemeral_state: OpOpenEphemeralState,
    op_new_rowid_state: OpNewRowidState,
    op_idx_insert_state: OpIdxInsertState,
    op_insert_state: OpInsertState,
    op_no_conflict_state: OpNoConflictState,
    seek_state: OpSeekState,
    /// Current collation sequence set by OP_CollSeq instruction
    current_collation: Option<CollationSeq>,
}

impl ProgramState {
    pub fn new(max_registers: usize, max_cursors: usize) -> Self {
        let cursors: RefCell<Vec<Option<Cursor>>> =
            RefCell::new((0..max_cursors).map(|_| None).collect());
        let registers = vec![Register::Value(Value::Null); max_registers];
        Self {
            pc: 0,
            cursors,
            registers,
            result_row: None,
            last_compare: None,
            deferred_seeks: vec![None; max_cursors],
            ended_coroutine: Bitfield::new(),
            once: SmallVec::<u32, 4>::new(),
            regex_cache: RegexCache::new(),
            mv_tx_id: None,
            interrupted: false,
            parameters: HashMap::new(),
            commit_state: CommitState::Ready,
            #[cfg(feature = "json")]
            json_cache: JsonCacheCell::new(),
            op_idx_delete_state: None,
            op_integrity_check_state: OpIntegrityCheckState::Start,
            op_open_ephemeral_state: OpOpenEphemeralState::Start,
            op_new_rowid_state: OpNewRowidState::Start,
            op_idx_insert_state: OpIdxInsertState::SeekIfUnique,
            op_insert_state: OpInsertState::Insert,
            op_no_conflict_state: OpNoConflictState::Start,
            seek_state: OpSeekState::Start,
            current_collation: None,
        }
    }

    pub fn column_count(&self) -> usize {
        self.registers.len()
    }

    pub fn column(&self, i: usize) -> Option<String> {
        Some(format!("{:?}", self.registers[i]))
    }

    pub fn interrupt(&mut self) {
        self.interrupted = true;
    }

    pub fn is_interrupted(&self) -> bool {
        self.interrupted
    }

    pub fn bind_at(&mut self, index: NonZero<usize>, value: Value) {
        self.parameters.insert(index, value);
    }

    pub fn get_parameter(&self, index: NonZero<usize>) -> Value {
        self.parameters.get(&index).cloned().unwrap_or(Value::Null)
    }

    pub fn reset(&mut self) {
        self.pc = 0;
        self.cursors.borrow_mut().iter_mut().for_each(|c| *c = None);
        self.registers
            .iter_mut()
            .for_each(|r| *r = Register::Value(Value::Null));
        self.last_compare = None;
        self.deferred_seeks.iter_mut().for_each(|s| *s = None);
        self.ended_coroutine.0 = [0; 4];
        self.regex_cache.like.clear();
        self.interrupted = false;
        self.parameters.clear();
        self.current_collation = None;
        #[cfg(feature = "json")]
        self.json_cache.clear()
    }

    pub fn get_cursor(&self, cursor_id: CursorID) -> std::cell::RefMut<Cursor> {
        let cursors = self.cursors.borrow_mut();
        std::cell::RefMut::map(cursors, |c| {
            c.get_mut(cursor_id)
                .unwrap_or_else(|| panic!("cursor id {cursor_id} out of bounds"))
                .as_mut()
                .unwrap_or_else(|| panic!("cursor id {cursor_id} is None"))
        })
    }
}

impl Register {
    pub fn get_owned_value(&self) -> &Value {
        match self {
            Register::Value(v) => v,
            Register::Record(r) => {
                assert!(!r.is_invalidated());
                r.as_blob_value()
            }
            _ => panic!("register holds unexpected value: {self:?}"),
        }
    }
}

#[macro_export]
macro_rules! must_be_btree_cursor {
    ($cursor_id:expr, $cursor_ref:expr, $state:expr, $insn_name:expr) => {{
        let (_, cursor_type) = $cursor_ref.get($cursor_id).unwrap();
        let cursor = match cursor_type {
            CursorType::BTreeTable(_) => $state.get_cursor($cursor_id),
            CursorType::BTreeIndex(_) => $state.get_cursor($cursor_id),
            CursorType::Pseudo(_) => panic!("{} on pseudo cursor", $insn_name),
            CursorType::Sorter => panic!("{} on sorter cursor", $insn_name),
            CursorType::VirtualTable(_) => panic!("{} on virtual table cursor", $insn_name),
        };
        cursor
    }};
}

pub struct Program {
    pub max_registers: usize,
    pub insns: Vec<(Insn, InsnFunction)>,
    pub cursor_ref: Vec<(Option<CursorKey>, CursorType)>,
    pub comments: Option<Vec<(InsnReference, &'static str)>>,
    pub parameters: crate::parameters::Parameters,
    pub connection: Arc<Connection>,
    pub n_change: Cell<i64>,
    pub change_cnt_on: bool,
    pub result_columns: Vec<ResultSetColumn>,
    pub table_references: TableReferences,
    pub sql: String,
    /// Whether the program accesses the database.
    /// Used to determine whether we need to check for schema changes when
    /// starting a transaction.
    pub accesses_db: bool,
}

impl Program {
    fn get_pager_from_database_index(&self, idx: &usize) -> Rc<Pager> {
        self.connection.get_pager_from_database_index(idx)
    }

    #[instrument(skip_all, level = Level::DEBUG)]
    pub fn step(
        &self,
        state: &mut ProgramState,
        mv_store: Option<Arc<MvStore>>,
        pager: Rc<Pager>,
    ) -> Result<StepResult> {
        loop {
            if self.connection.closed.get() {
                // Connection is closed for whatever reason, rollback the transaction.
                let state = self.connection.transaction_state.get();
                if let TransactionState::Write { schema_did_change } = state {
                    match pager.end_tx(true, schema_did_change, &self.connection, false)? {
                        IOResult::IO => return Ok(StepResult::IO),
                        IOResult::Done(_) => {}
                    }
                }
                return Err(LimboError::InternalError("Connection closed".to_string()));
            }
            if state.is_interrupted() {
                return Ok(StepResult::Interrupt);
            }
            // invalidate row
            let _ = state.result_row.take();
            let (insn, insn_function) = &self.insns[state.pc as usize];
            trace_insn(self, state.pc as InsnReference, insn);
            match insn_function(self, state, insn, &pager, mv_store.as_ref()) {
                Ok(InsnFunctionStepResult::Step) => {}
                Ok(InsnFunctionStepResult::Done) => return Ok(StepResult::Done),
                Ok(InsnFunctionStepResult::IO) => return Ok(StepResult::IO),
                Ok(InsnFunctionStepResult::Row) => return Ok(StepResult::Row),
                Ok(InsnFunctionStepResult::Interrupt) => return Ok(StepResult::Interrupt),
                Ok(InsnFunctionStepResult::Busy) => return Ok(StepResult::Busy),
                Err(err) => {
                    handle_program_error(&pager, &self.connection, &err)?;
                    return Err(err);
                }
            }
        }
    }

    #[instrument(skip_all, level = Level::DEBUG)]
    pub fn commit_txn(
        &self,
        pager: Rc<Pager>,
        program_state: &mut ProgramState,
        mv_store: Option<&Arc<MvStore>>,
        rollback: bool,
    ) -> Result<StepResult> {
        if self.connection.transaction_state.get() == TransactionState::None && mv_store.is_none() {
            // No need to do any work here if not in tx. Current MVCC logic doesn't work with this assumption,
            // hence the mv_store.is_none() check.
            return Ok(StepResult::Done);
        }
        if let Some(mv_store) = mv_store {
            let conn = self.connection.clone();
            let auto_commit = conn.auto_commit.get();
            if auto_commit {
                // FIXME: we don't want to commit stuff from other programs.
                let mut mv_transactions = conn.mv_transactions.borrow_mut();
                for tx_id in mv_transactions.iter() {
                    let mut state_machine =
                        mv_store.commit_tx(*tx_id, pager.clone(), &conn).unwrap();
                    state_machine
                        .step(mv_store)
                        .map_err(|e| LimboError::InternalError(e.to_string()))?;
                    assert!(state_machine.is_finalized());
                }
                mv_transactions.clear();
            }
            Ok(StepResult::Done)
        } else {
            let connection = self.connection.clone();
            let auto_commit = connection.auto_commit.get();
            tracing::trace!(
                "Halt auto_commit {}, state={:?}",
                auto_commit,
                program_state.commit_state
            );
            if program_state.commit_state == CommitState::Committing {
                let TransactionState::Write { schema_did_change } =
                    connection.transaction_state.get()
                else {
                    unreachable!("invalid state for write commit step")
                };
                self.step_end_write_txn(
                    &pager,
                    &mut program_state.commit_state,
                    &connection,
                    rollback,
                    schema_did_change,
                )
            } else if auto_commit {
                let current_state = connection.transaction_state.get();
                tracing::trace!("Auto-commit state: {:?}", current_state);
                match current_state {
                    TransactionState::Write { schema_did_change } => self.step_end_write_txn(
                        &pager,
                        &mut program_state.commit_state,
                        &connection,
                        rollback,
                        schema_did_change,
                    ),
                    TransactionState::Read => {
                        connection.transaction_state.replace(TransactionState::None);
                        pager.end_read_tx()?;
                        Ok(StepResult::Done)
                    }
                    TransactionState::None => Ok(StepResult::Done),
                    TransactionState::PendingUpgrade => {
                        panic!("Unexpected transaction state: {current_state:?} during auto-commit",)
                    }
                }
            } else {
                if self.change_cnt_on {
                    self.connection.set_changes(self.n_change.get());
                }
                Ok(StepResult::Done)
            }
        }
    }

    #[instrument(skip(self, pager, connection), level = Level::DEBUG)]
    fn step_end_write_txn(
        &self,
        pager: &Rc<Pager>,
        commit_state: &mut CommitState,
        connection: &Connection,
        rollback: bool,
        schema_did_change: bool,
    ) -> Result<StepResult> {
        let cacheflush_status = pager.end_tx(
            rollback,
            schema_did_change,
            connection,
            connection.wal_checkpoint_disabled.get(),
        )?;
        match cacheflush_status {
            IOResult::Done(_) => {
                if self.change_cnt_on {
                    self.connection.set_changes(self.n_change.get());
                }
                connection.transaction_state.replace(TransactionState::None);
                *commit_state = CommitState::Ready;
            }
            IOResult::IO => {
                tracing::trace!("Cacheflush IO");
                *commit_state = CommitState::Committing;
                return Ok(StepResult::IO);
            }
        }
        Ok(StepResult::Done)
    }

    #[rustfmt::skip]
    pub fn explain(&self) -> String {
        let mut buff = String::with_capacity(1024);
        buff.push_str("addr  opcode             p1    p2    p3    p4             p5  comment\n");
        buff.push_str("----  -----------------  ----  ----  ----  -------------  --  -------\n");
        let indent = "  ";
        let indent_counts = get_indent_counts(&self.insns);
        for (addr, (insn, _)) in self.insns.iter().enumerate() {
            let indent_count = indent_counts[addr];
            print_insn(
                self,
                addr as InsnReference,
                insn,
                indent.repeat(indent_count),
                &mut buff,
            );
            buff.push('\n');
        }
        buff
    }
}

fn make_record(registers: &[Register], start_reg: &usize, count: &usize) -> ImmutableRecord {
    let regs = &registers[*start_reg..*start_reg + *count];
    ImmutableRecord::from_registers(regs, regs.len())
}

pub fn registers_to_ref_values(registers: &[Register]) -> Vec<RefValue> {
    registers
        .iter()
        .map(|reg| {
            let value = reg.get_owned_value();
            match value {
                Value::Null => RefValue::Null,
                Value::Integer(i) => RefValue::Integer(*i),
                Value::Float(f) => RefValue::Float(*f),
                Value::Text(t) => RefValue::Text(TextRef {
                    value: RawSlice::new(t.value.as_ptr(), t.value.len()),
                    subtype: t.subtype,
                }),
                Value::Blob(b) => RefValue::Blob(RawSlice::new(b.as_ptr(), b.len())),
            }
        })
        .collect()
}

#[instrument(skip(program), level = Level::DEBUG)]
fn trace_insn(program: &Program, addr: InsnReference, insn: &Insn) {
    if !tracing::enabled!(tracing::Level::TRACE) {
        return;
    }
    tracing::trace!(
        "\n{}",
        explain::insn_to_str(
            program,
            addr,
            insn,
            String::new(),
            program.comments.as_ref().and_then(|comments| comments
                .iter()
                .find(|(offset, _)| *offset == addr)
                .map(|(_, comment)| comment)
                .copied())
        )
    );
}

fn print_insn(program: &Program, addr: InsnReference, insn: &Insn, indent: String, w: &mut String) {
    let s = explain::insn_to_str(
        program,
        addr,
        insn,
        indent,
        program.comments.as_ref().and_then(|comments| {
            comments
                .iter()
                .find(|(offset, _)| *offset == addr)
                .map(|(_, comment)| comment)
                .copied()
        }),
    );
    w.push_str(&s);
}

// The indenting rules are(from SQLite):
//
//  * For each "Next", "Prev", "VNext" or "VPrev" instruction, increase the ident number for
//    all opcodes that occur between the p2 jump destination and the opcode itself.
//
//   * Do the previous for "Return" instructions for when P2 is positive.
//
//   * For each "Goto", if the jump destination is earlier in the program and ends on one of:
//        Yield  SeekGt  SeekLt  RowSetRead  Rewind
//     or if the P1 parameter is one instead of zero, then increase the indent number for all
//     opcodes between the earlier instruction and "Goto"
fn get_indent_counts(insns: &[(Insn, InsnFunction)]) -> Vec<usize> {
    let mut indents = vec![0; insns.len()];

    for (i, (insn, _)) in insns.iter().enumerate() {
        let mut start = 0;
        let mut end = 0;
        match insn {
            Insn::Next { pc_if_next, .. } | Insn::VNext { pc_if_next, .. } => {
                let dest = pc_if_next.as_debug_int() as usize;
                if dest < i {
                    start = dest;
                    end = i;
                }
            }
            Insn::Prev { pc_if_prev, .. } => {
                let dest = pc_if_prev.as_debug_int() as usize;
                if dest < i {
                    start = dest;
                    end = i;
                }
            }

            Insn::Goto { target_pc } => {
                let dest = target_pc.as_debug_int() as usize;
                if dest < i
                    && matches!(
                        insns.get(dest).map(|(insn, _)| insn),
                        Some(Insn::Yield { .. })
                            | Some(Insn::SeekGT { .. })
                            | Some(Insn::SeekLT { .. })
                            | Some(Insn::Rewind { .. })
                    )
                {
                    start = dest;
                    end = i;
                }
            }

            _ => {}
        }
        for indent in indents.iter_mut().take(end).skip(start) {
            *indent += 1;
        }
    }

    indents
}

pub trait FromValueRow<'a> {
    fn from_value(value: &'a Value) -> Result<Self>
    where
        Self: Sized + 'a;
}

impl<'a> FromValueRow<'a> for i64 {
    fn from_value(value: &'a Value) -> Result<Self> {
        match value {
            Value::Integer(i) => Ok(*i),
            _ => Err(LimboError::ConversionError("Expected integer value".into())),
        }
    }
}

impl<'a> FromValueRow<'a> for f64 {
    fn from_value(value: &'a Value) -> Result<Self> {
        match value {
            Value::Float(f) => Ok(*f),
            _ => Err(LimboError::ConversionError("Expected integer value".into())),
        }
    }
}

impl<'a> FromValueRow<'a> for String {
    fn from_value(value: &'a Value) -> Result<Self> {
        match value {
            Value::Text(s) => Ok(s.as_str().to_string()),
            _ => Err(LimboError::ConversionError("Expected text value".into())),
        }
    }
}

impl<'a> FromValueRow<'a> for &'a str {
    fn from_value(value: &'a Value) -> Result<Self> {
        match value {
            Value::Text(s) => Ok(s.as_str()),
            _ => Err(LimboError::ConversionError("Expected text value".into())),
        }
    }
}

impl<'a> FromValueRow<'a> for &'a Value {
    fn from_value(value: &'a Value) -> Result<Self> {
        Ok(value)
    }
}

impl Row {
    pub fn get<'a, T: FromValueRow<'a> + 'a>(&'a self, idx: usize) -> Result<T> {
        let value = unsafe { self.values.add(idx).as_ref().unwrap() };
        let value = match value {
            Register::Value(owned_value) => owned_value,
            _ => unreachable!("a row should be formed of values only"),
        };
        T::from_value(value)
    }

    pub fn get_value(&self, idx: usize) -> &Value {
        let value = unsafe { self.values.add(idx).as_ref().unwrap() };
        match value {
            Register::Value(owned_value) => owned_value,
            _ => unreachable!("a row should be formed of values only"),
        }
    }

    pub fn get_values(&self) -> impl Iterator<Item = &Value> {
        let values = unsafe { std::slice::from_raw_parts(self.values, self.count) };
        // This should be ownedvalues
        // TODO: add check for this
        values.iter().map(|v| v.get_owned_value())
    }

    pub fn len(&self) -> usize {
        self.count
    }
}

/// Handle a program error by rolling back the transaction
pub fn handle_program_error(
    pager: &Rc<Pager>,
    connection: &Connection,
    err: &LimboError,
) -> Result<()> {
    match err {
        // Transaction errors, e.g. trying to start a nested transaction, do not cause a rollback.
        LimboError::TxError(_) => {}
        // Table locked errors, e.g. trying to checkpoint in an interactive transaction, do not cause a rollback.
        LimboError::TableLocked => {}
        _ => {
            let state = connection.transaction_state.get();
            if let TransactionState::Write { schema_did_change } = state {
                loop {
                    match pager.end_tx(true, schema_did_change, connection, false) {
                        Ok(IOResult::IO) => connection.run_once()?,
                        Ok(IOResult::Done(_)) => break,
                        Err(e) => {
                            tracing::error!("end_tx failed: {e}");
                            break;
                        }
                    }
                }
            } else if let Err(e) = pager.end_read_tx() {
                tracing::error!("end_read_tx failed: {e}");
            }
            connection.transaction_state.replace(TransactionState::None);
        }
    }
    Ok(())
}