Prefetch reader #18
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Prefetch reader #18
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kylebarron
commented
Feb 25, 2025
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| impl PrefetchReader { | ||
| pub async fn new(mut reader: Box<dyn AsyncFileReader>, prefetch: u64) -> Result<Self> { | ||
| let buffer = reader.get_bytes(0..prefetch).await?; |
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We pre-fetch this prefix of the file when "opening" this reader layer
kylebarron
commented
Feb 25, 2025
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| let usize_range = range.start as usize..range.end as usize; | ||
| let result = self.buffer.slice(usize_range); | ||
| async { Ok(result) }.boxed() |
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Then if the start and end of the requested range are fully within the existing cached buffer, we return that slice.
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Allows for fetching first X kb of a file, and then delegating further requests to this cached buffer.
This caused the Python file open to reduce from 2.5 minutes to 0.7sec
cc @geospatial-jeff. Because this is implemented as a middleware, we could implement whatever sort of cache we want here, like a block cache.