lance_file/v2/

writer.rs

// SPDX-License-Identifier: Apache-2.0
// SPDX-FileCopyrightText: Copyright The Lance Authors

use core::panic;
use std::collections::HashMap;
use std::sync::Arc;

use arrow_array::RecordBatch;

use arrow_data::ArrayData;
use bytes::{BufMut, Bytes, BytesMut};
use futures::stream::FuturesOrdered;
use futures::StreamExt;
use lance_core::datatypes::{Field, Schema as LanceSchema};
use lance_core::utils::bit::pad_bytes;
use lance_core::{Error, Result};
use lance_encoding::decoder::PageEncoding;
use lance_encoding::encoder::{
    default_encoding_strategy, BatchEncoder, EncodeTask, EncodedBatch, EncodedPage,
    EncodingOptions, FieldEncoder, FieldEncodingStrategy, OutOfLineBuffers,
};
use lance_encoding::repdef::RepDefBuilder;
use lance_encoding::version::LanceFileVersion;
use lance_io::object_writer::ObjectWriter;
use lance_io::traits::Writer;
use log::debug;
use prost::Message;
use prost_types::Any;
use snafu::{location, Location};
use tokio::io::AsyncWriteExt;
use tracing::instrument;

use crate::datatypes::FieldsWithMeta;
use crate::format::pb;
use crate::format::pbfile;
use crate::format::pbfile::DirectEncoding;
use crate::format::MAGIC;

/// Pages buffers are aligned to 64 bytes
pub(crate) const PAGE_BUFFER_ALIGNMENT: usize = 64;
const PAD_BUFFER: [u8; PAGE_BUFFER_ALIGNMENT] = [72; PAGE_BUFFER_ALIGNMENT];

#[derive(Debug, Clone, Default)]
pub struct FileWriterOptions {
    /// How many bytes to use for buffering column data
    ///
    /// When data comes in small batches the writer will buffer column data so that
    /// larger pages can be created.  This value will be divided evenly across all of the
    /// columns.  Generally you want this to be at least large enough to match your
    /// filesystem's ideal read size per column.
    ///
    /// In some cases you might want this value to be even larger if you have highly
    /// compressible data.  However, if this is too large, then the writer could require
    /// a lot of memory and write performance may suffer if the CPU-expensive encoding
    /// falls behind and can't be interleaved with the I/O expensive flushing.
    ///
    /// The default will use 8MiB per column which should be reasonable for most cases.
    // TODO: Do we need to be able to set this on a per-column basis?
    pub data_cache_bytes: Option<u64>,
    /// A hint to indicate the max size of a page
    ///
    /// This hint can't always be respected.  A single value could be larger than this value
    /// and we never slice single values.  In addition, there are some cases where it can be
    /// difficult to know size up-front and so we might not be able to respect this value.
    pub max_page_bytes: Option<u64>,
    /// The file writer buffers columns until enough data has arrived to flush a page
    /// to disk.
    ///
    /// Some columns with small data types may not flush very often.  These arrays can
    /// stick around for a long time.  These arrays might also be keeping larger data
    /// structures alive.  By default, the writer will make a deep copy of this array
    /// to avoid any potential memory leaks.  However, this can be disabled for a
    /// (probably minor) performance boost if you are sure that arrays are not keeping
    /// any sibling structures alive (this typically means the array was allocated in
    /// the same language / runtime as the writer)
    ///
    /// Do not enable this if your data is arriving from the C data interface.
    /// Data typically arrives one "batch" at a time (encoded in the C data interface
    /// as a struct array).  Each array in that batch keeps the entire batch alive.
    /// This means a small boolean array (which we will buffer in memory for quite a
    /// while) might keep a much larger record batch around in memory (even though most
    /// of that batch's data has been written to disk)
    pub keep_original_array: Option<bool>,
    pub encoding_strategy: Option<Arc<dyn FieldEncodingStrategy>>,
    /// The format version to use when writing the file
    ///
    /// This controls which encodings will be used when encoding the data.  Newer
    /// versions may have more efficient encodings.  However, newer format versions will
    /// require more up-to-date readers to read the data.
    pub format_version: Option<LanceFileVersion>,
}

pub struct FileWriter {
    writer: ObjectWriter,
    schema: Option<LanceSchema>,
    column_writers: Vec<Box<dyn FieldEncoder>>,
    column_metadata: Vec<pbfile::ColumnMetadata>,
    field_id_to_column_indices: Vec<(u32, u32)>,
    num_columns: u32,
    rows_written: u64,
    global_buffers: Vec<(u64, u64)>,
    schema_metadata: HashMap<String, String>,
    options: FileWriterOptions,
}

fn initial_column_metadata() -> pbfile::ColumnMetadata {
    pbfile::ColumnMetadata {
        pages: Vec::new(),
        buffer_offsets: Vec::new(),
        buffer_sizes: Vec::new(),
        encoding: None,
    }
}

impl FileWriter {
    /// Create a new FileWriter with a desired output schema
    pub fn try_new(
        object_writer: ObjectWriter,
        schema: LanceSchema,
        options: FileWriterOptions,
    ) -> Result<Self> {
        let mut writer = Self::new_lazy(object_writer, options);
        writer.initialize(schema)?;
        Ok(writer)
    }

    /// Create a new FileWriter without a desired output schema
    ///
    /// The output schema will be set based on the first batch of data to arrive.
    /// If no data arrives and the writer is finished then the write will fail.
    pub fn new_lazy(object_writer: ObjectWriter, options: FileWriterOptions) -> Self {
        Self {
            writer: object_writer,
            schema: None,
            column_writers: Vec::new(),
            column_metadata: Vec::new(),
            num_columns: 0,
            rows_written: 0,
            field_id_to_column_indices: Vec::new(),
            global_buffers: Vec::new(),
            schema_metadata: HashMap::new(),
            options,
        }
    }

    async fn do_write_buffer(writer: &mut ObjectWriter, buf: &[u8]) -> Result<()> {
        writer.write_all(buf).await?;
        let pad_bytes = pad_bytes::<PAGE_BUFFER_ALIGNMENT>(buf.len());
        writer.write_all(&PAD_BUFFER[..pad_bytes]).await?;
        Ok(())
    }

    /// Returns the format version that will be used when writing the file
    pub fn version(&self) -> LanceFileVersion {
        self.options.format_version.unwrap_or_default()
    }

    async fn write_page(&mut self, encoded_page: EncodedPage) -> Result<()> {
        let buffers = encoded_page.data;
        let mut buffer_offsets = Vec::with_capacity(buffers.len());
        let mut buffer_sizes = Vec::with_capacity(buffers.len());
        for buffer in buffers {
            buffer_offsets.push(self.writer.tell().await? as u64);
            buffer_sizes.push(buffer.len() as u64);
            Self::do_write_buffer(&mut self.writer, &buffer).await?;
        }
        let encoded_encoding = match encoded_page.description {
            PageEncoding::Legacy(array_encoding) => Any::from_msg(&array_encoding)?.encode_to_vec(),
            PageEncoding::Structural(page_layout) => Any::from_msg(&page_layout)?.encode_to_vec(),
        };
        let page = pbfile::column_metadata::Page {
            buffer_offsets,
            buffer_sizes,
            encoding: Some(pbfile::Encoding {
                location: Some(pbfile::encoding::Location::Direct(DirectEncoding {
                    encoding: encoded_encoding,
                })),
            }),
            length: encoded_page.num_rows,
            priority: encoded_page.row_number,
        };
        self.column_metadata[encoded_page.column_idx as usize]
            .pages
            .push(page);
        Ok(())
    }

    #[instrument(skip_all, level = "debug")]
    async fn write_pages(&mut self, mut encoding_tasks: FuturesOrdered<EncodeTask>) -> Result<()> {
        // As soon as an encoding task is done we write it.  There is no parallelism
        // needed here because "writing" is really just submitting the buffer to the
        // underlying write scheduler (either the OS or object_store's scheduler for
        // cloud writes).  The only time we might truly await on write_page is if the
        // scheduler's write queue is full.
        //
        // Also, there is no point in trying to make write_page parallel anyways
        // because we wouldn't want buffers getting mixed up across pages.
        while let Some(encoding_task) = encoding_tasks.next().await {
            let encoded_page = encoding_task?;
            self.write_page(encoded_page).await?;
        }
        // It's important to flush here, we don't know when the next batch will arrive
        // and the underlying cloud store could have writes in progress that won't advance
        // until we interact with the writer again.  These in-progress writes will time out
        // if we don't flush.
        self.writer.flush().await?;
        Ok(())
    }

    /// Schedule batches of data to be written to the file
    pub async fn write_batches(
        &mut self,
        batches: impl Iterator<Item = &RecordBatch>,
    ) -> Result<()> {
        for batch in batches {
            self.write_batch(batch).await?;
        }
        Ok(())
    }

    fn verify_field_nullability(arr: &ArrayData, field: &Field) -> Result<()> {
        if !field.nullable && arr.null_count() > 0 {
            return Err(Error::invalid_input(format!("The field `{}` contained null values even though the field is marked non-null in the schema", field.name), location!()));
        }

        for (child_field, child_arr) in field.children.iter().zip(arr.child_data()) {
            Self::verify_field_nullability(child_arr, child_field)?;
        }

        Ok(())
    }

    fn verify_nullability_constraints(&self, batch: &RecordBatch) -> Result<()> {
        for (col, field) in batch
            .columns()
            .iter()
            .zip(self.schema.as_ref().unwrap().fields.iter())
        {
            Self::verify_field_nullability(&col.to_data(), field)?;
        }
        Ok(())
    }

    fn initialize(&mut self, mut schema: LanceSchema) -> Result<()> {
        let cache_bytes_per_column = if let Some(data_cache_bytes) = self.options.data_cache_bytes {
            data_cache_bytes / schema.fields.len() as u64
        } else {
            8 * 1024 * 1024
        };

        let max_page_bytes = self.options.max_page_bytes.unwrap_or(32 * 1024 * 1024);

        schema.validate()?;

        let keep_original_array = self.options.keep_original_array.unwrap_or(false);
        let encoding_strategy = self.options.encoding_strategy.clone().unwrap_or_else(|| {
            let version = self.version();
            default_encoding_strategy(version).into()
        });

        let encoding_options = EncodingOptions {
            cache_bytes_per_column,
            max_page_bytes,
            keep_original_array,
            buffer_alignment: PAGE_BUFFER_ALIGNMENT as u64,
        };
        let encoder =
            BatchEncoder::try_new(&schema, encoding_strategy.as_ref(), &encoding_options)?;
        self.num_columns = encoder.num_columns();

        self.column_writers = encoder.field_encoders;
        self.column_metadata = vec![initial_column_metadata(); self.num_columns as usize];
        self.field_id_to_column_indices = encoder.field_id_to_column_index;
        self.schema_metadata
            .extend(std::mem::take(&mut schema.metadata));
        self.schema = Some(schema);
        Ok(())
    }

    fn ensure_initialized(&mut self, batch: &RecordBatch) -> Result<&LanceSchema> {
        if self.schema.is_none() {
            let schema = LanceSchema::try_from(batch.schema().as_ref())?;
            self.initialize(schema)?;
        }
        Ok(self.schema.as_ref().unwrap())
    }

    #[instrument(skip_all, level = "debug")]
    fn encode_batch(
        &mut self,
        batch: &RecordBatch,
        external_buffers: &mut OutOfLineBuffers,
    ) -> Result<Vec<Vec<EncodeTask>>> {
        self.schema
            .as_ref()
            .unwrap()
            .fields
            .iter()
            .zip(self.column_writers.iter_mut())
            .map(|(field, column_writer)| {
                let array = batch
                    .column_by_name(&field.name)
                    .ok_or(Error::InvalidInput {
                        source: format!(
                            "Cannot write batch.  The batch was missing the column `{}`",
                            field.name
                        )
                        .into(),
                        location: location!(),
                    })?;
                let repdef = RepDefBuilder::default();
                column_writer.maybe_encode(
                    array.clone(),
                    external_buffers,
                    repdef,
                    self.rows_written,
                )
            })
            .collect::<Result<Vec<_>>>()
    }

    /// Schedule a batch of data to be written to the file
    ///
    /// Note: the future returned by this method may complete before the data has been fully
    /// flushed to the file (some data may be in the data cache or the I/O cache)
    pub async fn write_batch(&mut self, batch: &RecordBatch) -> Result<()> {
        debug!(
            "write_batch called with {} bytes of data",
            batch.get_array_memory_size()
        );
        self.ensure_initialized(batch)?;
        self.verify_nullability_constraints(batch)?;
        let num_rows = batch.num_rows() as u64;
        if num_rows == 0 {
            return Ok(());
        }
        if num_rows > u32::MAX as u64 {
            return Err(Error::InvalidInput {
                source: "cannot write Lance files with more than 2^32 rows".into(),
                location: location!(),
            });
        }
        // First we push each array into its column writer.  This may or may not generate enough
        // data to trigger an encoding task.  We collect any encoding tasks into a queue.
        let mut external_buffers =
            OutOfLineBuffers::new(self.tell().await?, PAGE_BUFFER_ALIGNMENT as u64);
        let encoding_tasks = self.encode_batch(batch, &mut external_buffers)?;
        // Next, write external buffers
        for external_buffer in external_buffers.take_buffers() {
            Self::do_write_buffer(&mut self.writer, &external_buffer).await?;
        }

        let encoding_tasks = encoding_tasks
            .into_iter()
            .flatten()
            .collect::<FuturesOrdered<_>>();

        self.rows_written = match self.rows_written.checked_add(batch.num_rows() as u64) {
            Some(rows_written) => rows_written,
            None => {
                return Err(Error::InvalidInput { source: format!("cannot write batch with {} rows because {} rows have already been written and Lance files cannot contain more than 2^64 rows", num_rows, self.rows_written).into(), location: location!() });
            }
        };

        self.write_pages(encoding_tasks).await?;

        Ok(())
    }

    async fn write_column_metadata(
        &mut self,
        metadata: pbfile::ColumnMetadata,
    ) -> Result<(u64, u64)> {
        let metadata_bytes = metadata.encode_to_vec();
        let position = self.writer.tell().await? as u64;
        let len = metadata_bytes.len() as u64;
        self.writer.write_all(&metadata_bytes).await?;
        Ok((position, len))
    }

    async fn write_column_metadatas(&mut self) -> Result<Vec<(u64, u64)>> {
        let mut metadatas = Vec::new();
        std::mem::swap(&mut self.column_metadata, &mut metadatas);
        let mut metadata_positions = Vec::with_capacity(metadatas.len());
        for metadata in metadatas {
            metadata_positions.push(self.write_column_metadata(metadata).await?);
        }
        Ok(metadata_positions)
    }

    fn make_file_descriptor(
        schema: &lance_core::datatypes::Schema,
        num_rows: u64,
    ) -> Result<pb::FileDescriptor> {
        let fields_with_meta = FieldsWithMeta::from(schema);
        Ok(pb::FileDescriptor {
            schema: Some(pb::Schema {
                fields: fields_with_meta.fields.0,
                metadata: fields_with_meta.metadata,
            }),
            length: num_rows,
        })
    }

    async fn write_global_buffers(&mut self) -> Result<Vec<(u64, u64)>> {
        let schema = self.schema.as_mut().ok_or(Error::invalid_input("No schema provided on writer open and no data provided.  Schema is unknown and file cannot be created", location!()))?;
        schema.metadata = std::mem::take(&mut self.schema_metadata);
        let file_descriptor = Self::make_file_descriptor(schema, self.rows_written)?;
        let file_descriptor_bytes = file_descriptor.encode_to_vec();
        let file_descriptor_len = file_descriptor_bytes.len() as u64;
        let file_descriptor_position = self.writer.tell().await? as u64;
        self.writer.write_all(&file_descriptor_bytes).await?;
        let mut gbo_table = Vec::with_capacity(1 + self.global_buffers.len());
        gbo_table.push((file_descriptor_position, file_descriptor_len));
        gbo_table.append(&mut self.global_buffers);
        Ok(gbo_table)
    }

    /// Add a metadata entry to the schema
    ///
    /// This method is useful because sometimes the metadata is not known until after the
    /// data has been written.  This method allows you to alter the schema metadata.  It
    /// must be called before `finish` is called.
    pub fn add_schema_metadata(&mut self, key: impl Into<String>, value: impl Into<String>) {
        self.schema_metadata.insert(key.into(), value.into());
    }

    /// Adds a global buffer to the file
    ///
    /// The global buffer can contain any arbitrary bytes.  It will be written to the disk
    /// immediately.  This method returns the index of the global buffer (this will always
    /// start at 1 and increment by 1 each time this method is called)
    pub async fn add_global_buffer(&mut self, buffer: Bytes) -> Result<u32> {
        let position = self.writer.tell().await? as u64;
        let len = buffer.len() as u64;
        Self::do_write_buffer(&mut self.writer, &buffer).await?;
        self.global_buffers.push((position, len));
        Ok(self.global_buffers.len() as u32)
    }

    async fn finish_writers(&mut self) -> Result<()> {
        let mut col_idx = 0;
        for mut writer in std::mem::take(&mut self.column_writers) {
            let mut external_buffers =
                OutOfLineBuffers::new(self.tell().await?, PAGE_BUFFER_ALIGNMENT as u64);
            let columns = writer.finish(&mut external_buffers).await?;
            for buffer in external_buffers.take_buffers() {
                self.writer.write_all(&buffer).await?;
            }
            debug_assert_eq!(
                columns.len(),
                writer.num_columns() as usize,
                "Expected {} columns from column at index {} and got {}",
                writer.num_columns(),
                col_idx,
                columns.len()
            );
            for column in columns {
                for page in column.final_pages {
                    self.write_page(page).await?;
                }
                let column_metadata = &mut self.column_metadata[col_idx];
                let mut buffer_pos = self.writer.tell().await? as u64;
                for buffer in column.column_buffers {
                    column_metadata.buffer_offsets.push(buffer_pos);
                    let mut size = 0;
                    Self::do_write_buffer(&mut self.writer, &buffer).await?;
                    size += buffer.len() as u64;
                    buffer_pos += size;
                    column_metadata.buffer_sizes.push(size);
                }
                let encoded_encoding = Any::from_msg(&column.encoding)?.encode_to_vec();
                column_metadata.encoding = Some(pbfile::Encoding {
                    location: Some(pbfile::encoding::Location::Direct(pbfile::DirectEncoding {
                        encoding: encoded_encoding,
                    })),
                });
                col_idx += 1;
            }
        }
        if col_idx != self.column_metadata.len() {
            panic!(
                "Column writers finished with {} columns but we expected {}",
                col_idx,
                self.column_metadata.len()
            );
        }
        Ok(())
    }

    /// Converts self.version (which is a mix of "software version" and
    /// "format version" into a format version)
    fn version_to_numbers(&self) -> (u16, u16) {
        let version = self.options.format_version.unwrap_or_default();
        match version.resolve() {
            LanceFileVersion::V2_0 => (0, 3),
            LanceFileVersion::V2_1 => (2, 1),
            _ => panic!("Unsupported version: {}", version),
        }
    }

    /// Finishes writing the file
    ///
    /// This method will wait until all data has been flushed to the file.  Then it
    /// will write the file metadata and the footer.  It will not return until all
    /// data has been flushed and the file has been closed.
    ///
    /// Returns the total number of rows written
    pub async fn finish(&mut self) -> Result<u64> {
        // 1. flush any remaining data and write out those pages
        let mut external_buffers =
            OutOfLineBuffers::new(self.tell().await?, PAGE_BUFFER_ALIGNMENT as u64);
        let encoding_tasks = self
            .column_writers
            .iter_mut()
            .map(|writer| writer.flush(&mut external_buffers))
            .collect::<Result<Vec<_>>>()?;
        for external_buffer in external_buffers.take_buffers() {
            Self::do_write_buffer(&mut self.writer, &external_buffer).await?;
        }
        let encoding_tasks = encoding_tasks
            .into_iter()
            .flatten()
            .collect::<FuturesOrdered<_>>();
        self.write_pages(encoding_tasks).await?;

        self.finish_writers().await?;

        // 3. write global buffers (we write the schema here)
        let global_buffer_offsets = self.write_global_buffers().await?;
        let num_global_buffers = global_buffer_offsets.len() as u32;

        // 4. write the column metadatas
        let column_metadata_start = self.writer.tell().await? as u64;
        let metadata_positions = self.write_column_metadatas().await?;

        // 5. write the column metadata offset table
        let cmo_table_start = self.writer.tell().await? as u64;
        for (meta_pos, meta_len) in metadata_positions {
            self.writer.write_u64_le(meta_pos).await?;
            self.writer.write_u64_le(meta_len).await?;
        }

        // 6. write global buffers offset table
        let gbo_table_start = self.writer.tell().await? as u64;
        for (gbo_pos, gbo_len) in global_buffer_offsets {
            self.writer.write_u64_le(gbo_pos).await?;
            self.writer.write_u64_le(gbo_len).await?;
        }

        let (major, minor) = self.version_to_numbers();
        // 7. write the footer
        self.writer.write_u64_le(column_metadata_start).await?;
        self.writer.write_u64_le(cmo_table_start).await?;
        self.writer.write_u64_le(gbo_table_start).await?;
        self.writer.write_u32_le(num_global_buffers).await?;
        self.writer.write_u32_le(self.num_columns).await?;
        self.writer.write_u16_le(major).await?;
        self.writer.write_u16_le(minor).await?;
        self.writer.write_all(MAGIC).await?;

        // 7. close the writer
        self.writer.shutdown().await?;
        Ok(self.rows_written)
    }

    pub async fn tell(&mut self) -> Result<u64> {
        Ok(self.writer.tell().await? as u64)
    }

    pub fn field_id_to_column_indices(&self) -> &[(u32, u32)] {
        &self.field_id_to_column_indices
    }
}

/// Utility trait for converting EncodedBatch to Bytes using the
/// lance file format
pub trait EncodedBatchWriteExt {
    /// Serializes into a lance file, including the schema
    fn try_to_self_described_lance(&self) -> Result<Bytes>;
    /// Serializes into a lance file, without the schema.
    ///
    /// The schema must be provided to deserialize the buffer
    fn try_to_mini_lance(&self) -> Result<Bytes>;
}

// Creates a lance footer and appends it to the encoded data
//
// The logic here is very similar to logic in the FileWriter except we
// are using BufMut (put_xyz) instead of AsyncWrite (write_xyz).
fn concat_lance_footer(batch: &EncodedBatch, write_schema: bool) -> Result<Bytes> {
    // Estimating 1MiB for file footer
    let mut data = BytesMut::with_capacity(batch.data.len() + 1024 * 1024);
    data.put(batch.data.clone());
    // write global buffers (we write the schema here)
    let global_buffers = if write_schema {
        let schema_start = data.len() as u64;
        let lance_schema = lance_core::datatypes::Schema::try_from(batch.schema.as_ref())?;
        let descriptor = FileWriter::make_file_descriptor(&lance_schema, batch.num_rows)?;
        let descriptor_bytes = descriptor.encode_to_vec();
        let descriptor_len = descriptor_bytes.len() as u64;
        data.put(descriptor_bytes.as_slice());

        vec![(schema_start, descriptor_len)]
    } else {
        vec![]
    };
    let col_metadata_start = data.len() as u64;

    let mut col_metadata_positions = Vec::new();
    // Write column metadata
    for col in &batch.page_table {
        let position = data.len() as u64;
        let pages = col
            .page_infos
            .iter()
            .map(|page_info| {
                let encoded_encoding = match &page_info.encoding {
                    PageEncoding::Legacy(array_encoding) => {
                        Any::from_msg(array_encoding)?.encode_to_vec()
                    }
                    PageEncoding::Structural(page_layout) => {
                        Any::from_msg(page_layout)?.encode_to_vec()
                    }
                };
                let (buffer_offsets, buffer_sizes): (Vec<_>, Vec<_>) = page_info
                    .buffer_offsets_and_sizes
                    .as_ref()
                    .iter()
                    .cloned()
                    .unzip();
                Ok(pbfile::column_metadata::Page {
                    buffer_offsets,
                    buffer_sizes,
                    encoding: Some(pbfile::Encoding {
                        location: Some(pbfile::encoding::Location::Direct(DirectEncoding {
                            encoding: encoded_encoding,
                        })),
                    }),
                    length: page_info.num_rows,
                    priority: page_info.priority,
                })
            })
            .collect::<Result<Vec<_>>>()?;
        let (buffer_offsets, buffer_sizes): (Vec<_>, Vec<_>) =
            col.buffer_offsets_and_sizes.iter().cloned().unzip();
        let encoded_col_encoding = Any::from_msg(&col.encoding)?.encode_to_vec();
        let column = pbfile::ColumnMetadata {
            pages,
            buffer_offsets,
            buffer_sizes,
            encoding: Some(pbfile::Encoding {
                location: Some(pbfile::encoding::Location::Direct(pbfile::DirectEncoding {
                    encoding: encoded_col_encoding,
                })),
            }),
        };
        let column_bytes = column.encode_to_vec();
        col_metadata_positions.push((position, column_bytes.len() as u64));
        data.put(column_bytes.as_slice());
    }
    // Write column metadata offsets table
    let cmo_table_start = data.len() as u64;
    for (meta_pos, meta_len) in col_metadata_positions {
        data.put_u64_le(meta_pos);
        data.put_u64_le(meta_len);
    }
    // Write global buffers offsets table
    let gbo_table_start = data.len() as u64;
    let num_global_buffers = global_buffers.len() as u32;
    for (gbo_pos, gbo_len) in global_buffers {
        data.put_u64_le(gbo_pos);
        data.put_u64_le(gbo_len);
    }

    let (major, minor) = LanceFileVersion::default().to_numbers();

    // write the footer
    data.put_u64_le(col_metadata_start);
    data.put_u64_le(cmo_table_start);
    data.put_u64_le(gbo_table_start);
    data.put_u32_le(num_global_buffers);
    data.put_u32_le(batch.page_table.len() as u32);
    data.put_u16_le(major as u16);
    data.put_u16_le(minor as u16);
    data.put(MAGIC.as_slice());

    Ok(data.freeze())
}

impl EncodedBatchWriteExt for EncodedBatch {
    fn try_to_self_described_lance(&self) -> Result<Bytes> {
        concat_lance_footer(self, true)
    }

    fn try_to_mini_lance(&self) -> Result<Bytes> {
        concat_lance_footer(self, false)
    }
}

#[cfg(test)]
mod tests {
    use std::sync::Arc;

    use arrow_array::{types::Float64Type, RecordBatchReader};
    use lance_datagen::{array, gen, BatchCount, RowCount};
    use lance_io::object_store::ObjectStore;
    use object_store::path::Path;

    use crate::v2::writer::{FileWriter, FileWriterOptions};

    #[tokio::test]
    async fn test_basic_write() {
        let tmp_dir = tempfile::tempdir().unwrap();
        let tmp_path: String = tmp_dir.path().to_str().unwrap().to_owned();
        let tmp_path = Path::parse(tmp_path).unwrap();
        let tmp_path = tmp_path.child("some_file.lance");
        let obj_store = Arc::new(ObjectStore::local());

        let reader = gen()
            .col("score", array::rand::<Float64Type>())
            .into_reader_rows(RowCount::from(1000), BatchCount::from(10));

        let writer = obj_store.create(&tmp_path).await.unwrap();

        let lance_schema =
            lance_core::datatypes::Schema::try_from(reader.schema().as_ref()).unwrap();

        let mut file_writer =
            FileWriter::try_new(writer, lance_schema, FileWriterOptions::default()).unwrap();

        for batch in reader {
            file_writer.write_batch(&batch.unwrap()).await.unwrap();
        }
        file_writer.add_schema_metadata("foo", "bar");
        file_writer.finish().await.unwrap();
        // Tests asserting the contents of the written file are in reader.rs
    }

    #[tokio::test]
    async fn test_write_empty() {
        let tmp_dir = tempfile::tempdir().unwrap();
        let tmp_path: String = tmp_dir.path().to_str().unwrap().to_owned();
        let tmp_path = Path::parse(tmp_path).unwrap();
        let tmp_path = tmp_path.child("some_file.lance");
        let obj_store = Arc::new(ObjectStore::local());

        let reader = gen()
            .col("score", array::rand::<Float64Type>())
            .into_reader_rows(RowCount::from(0), BatchCount::from(0));

        let writer = obj_store.create(&tmp_path).await.unwrap();

        let lance_schema =
            lance_core::datatypes::Schema::try_from(reader.schema().as_ref()).unwrap();

        let mut file_writer =
            FileWriter::try_new(writer, lance_schema, FileWriterOptions::default()).unwrap();

        for batch in reader {
            file_writer.write_batch(&batch.unwrap()).await.unwrap();
        }
        file_writer.add_schema_metadata("foo", "bar");
        file_writer.finish().await.unwrap();
    }
}