Trait HummockIterator

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pub trait HummockIterator: Send {
    type Direction: HummockIteratorDirection;

    // Required methods
    fn next(&mut self) -> impl Future<Output = HummockResult<()>> + Send + '_;
    fn key(&self) -> FullKey<&[u8]>;
    fn value(&self) -> HummockValue<&[u8]>;
    fn is_valid(&self) -> bool;
    fn rewind(&mut self) -> impl Future<Output = HummockResult<()>> + Send + '_;
    fn seek<'a>(
        &'a mut self,
        key: FullKey<&'a [u8]>,
    ) -> impl Future<Output = HummockResult<()>> + Send;
    fn collect_local_statistic(&self, _stats: &mut StoreLocalStatistic);
    fn value_meta(&self) -> ValueMeta;
}

Expand description

HummockIterator defines the interface of all iterators, including SstableIterator, MergeIterator, UserIterator and ConcatIterator.

After creating the iterator instance,

if you want to iterate from the beginning, you need to then call its rewind method.
if you want to iterate from some specific position, you need to then call its seek method.

Required Associated Types§

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type Direction: HummockIteratorDirection

Required Methods§

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fn next(&mut self) -> impl Future<Output = HummockResult<()>> + Send + '_

Moves a valid iterator to the next key.

Note:

Before calling this function, makes sure the iterator is_valid.
After calling this function, you may first check whether the iterator is_valid again, then get the new data by calling key and value.
If the position after calling this is invalid, this function WON’T return an Err. You should check is_valid before continuing the iteration.

§Panics

This function will panic if the iterator is invalid.

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fn key(&self) -> FullKey<&[u8]>

Retrieves the current key.

Note:

Before calling this function, makes sure the iterator is_valid.
This function should be straightforward and return immediately.

§Panics

This function will panic if the iterator is invalid.

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fn value(&self) -> HummockValue<&[u8]>

Retrieves the current value, decoded as HummockValue.

Note:

Before calling this function, makes sure the iterator is_valid.
This function should be straightforward and return immediately.

§Panics

This function will panic if the iterator is invalid, or the value cannot be decoded into HummockValue.

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fn is_valid(&self) -> bool

Indicates whether the iterator can be used.

Note:

ONLY call key, value, and next if is_valid returns true.
This function should be straightforward and return immediately.

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fn rewind(&mut self) -> impl Future<Output = HummockResult<()>> + Send + '_

Resets the position of the iterator.

Note:

Do not decide whether the position is valid or not by checking the returned error of this function. This function WON’T return an Err if invalid. You should check is_valid before starting iteration.

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fn seek<'a>( &'a mut self, key: FullKey<&'a [u8]>, ) -> impl Future<Output = HummockResult<()>> + Send

Resets iterator and seeks to the first position where the key >= provided key, or key <= provided key if this is a backward iterator.

Note:

Do not decide whether the position is valid or not by checking the returned error of this function. This function WON’T return an Err if invalid. You should check is_valid before starting iteration.

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