You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: mod.rs
    path of file: ./repos/fjall/src/batch
    
    the code of the file until where you have to start completion: pub mod item;

use crate::{Keyspace, PartitionHandle};
use item::Item;
use lsm_tree::{Value, ValueType};
use std::{
    collections::{HashMap, HashSet},
    sync::Arc,
};

/// Partition key (a.k.a. column family, locality group)
pub type PartitionKey = Arc<str>;

/// An atomic write batch
///
/// Allows atomically writing across partitions inside the tree.
pub struct Batch {
    data: Vec<Item>,
    keyspace: Keyspace,
}

impl Batch {
    /// Initializes a new write batch
    /// This function is called by [`Keyspace::batch`]
    pub(crate) fn new(keyspace: Keyspace) -> Self {
        Self {
            data: Vec::with_capacity(100),
            keyspace,
        }
    }

    /// Inserts a key-value pair into the batch
    pub fn insert<K: AsRef<[u8]>, V: AsRef<[u8]>>(
        &mut self,
        p: &PartitionHandle,
        key: K,
        value: V,
    ) {
        self.data.push(Item::new(
            p.name.clone(),
            key.as_ref(),
            value.as_ref(),
            ValueType::Value,
        ));
    }

    /// Adds a tombstone marker for a key
    pub fn remove<K: AsRef<[u8]>>(&mut self, p: &PartitionHandle, key: K) {
        self.data.push(Item::new(
            p.name.clone(),
            key.as_ref(),
            vec![],
            ValueType::Tombstone,
        ));
    }

    /// Commits the batch to the LSM-tree atomically.
    ///
    /// # Errors
    ///
    /// Will return `Err` if an IO error occurs.
    pub fn commit(mut self) -> crate::Result<()> {
        log::trace!("batch: Acquiring shard");
        let mut shard = self.keyspace.journal.get_writer();

        // NOTE: Fully (write) lock
    
    pub fn commit(mut self) -> crate::Result<()> {
        log::trace!("batch: Acquiring shard");
        let mut shard = self.keyspace.journal.get_writer();

        // NOTE: Fully (write) lock, so the batch can be committed atomically
        log::trace!("batch: Acquiring partitions lock");
        let partitions = self.keyspace.partitions.write().expect("lock is poisoned");

        // IMPORTANT: Need to WRITE lock all affected partition's memtables
        // Otherwise, there may be read skew
        log::trace!("batch: Acquiring memtable locks");
        let locked_memtables = {
            let mut lock_map = HashMap::new();

            for item in &self.data {
                if lock_map.contains_key(&item.partition) {
                    continue;
                }

                let Some(partition) = partitions.get(&item.partition) else {
                    continue;
                };

                lock_map.insert(
                    item.partition.clone(),
                    partition.tree.lock_active_memtable(),
                );
            }

            lock_map
        };

        let batch_seqno = self.keyspace.seqno.next();

        let items = self.data.iter().collect::<Vec<_>>();
        let _ = shard.writer.write_batch(&items, batch_seqno)?;

        let mut partitions_with_possible_stall = HashSet::new();

        let mut batch_size = 0u64;

        log::trace!("Applying {} batched items to memtable(s)", self.data.len());
        for item in std::mem::take(&mut self.data) {
            let Some(partition) = partitions.get(&item.partition) else {
                continue;
            };

            let Some(active_memtable) = locked_memtables.get(&item.partition) else {
                continue;
            };

            let value = Value {
                key: item.key,
                value: item.value,
                seqno: batch_seqno,
                value_type: item.value_type,
            };

            let (item_size, _) = active_memtable.insert(value);
            batch_size += u64::from(item_size);

            // IMPORTANT: Clone the handle, because we don't want to keep the partitions lock open
            partitions_with_possible_stall.insert(partition.clone());
        }

        drop(locked_memtables);
        drop(partitions);
        drop(shard);

        // IMPORTANT: Add batch size to current write buffer size
        // Otherwise write buffer growth is unbounded when using batches
        self.keyspace.write_buffer_manager.allocate(batch_size);

        // Check each affected partition for write stall/halt
        for partition in partitions_with_possible_stall {
            let memtable_size = partition.tree.active_memtable_size();

            if let Err(e) = partition.check_memtable_overflow(memtable_size) {
                log::error!("Failed memtable rotate check: {e:?}");
            };

            // IMPORTANT: Check write buffer as well
            // Otherwise batch writes are never stalled/halted
            let write_buffer_size = self.keyspace.write_buffer_manager.get();
            partition.check_write_buffer_size(write_buffer_size);
        }

        Ok(())
    }