Reuse the same reader across ReadChunk calls so that prefetched blocks are not discared. #82
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
![copybara-service[bot]](https://avatars.githubusercontent.com/in/44061?s=60&v=4){kind=small}
|
Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA). View this failed invocation of the CLA check for more information. For the most up to date status, view the checks section at the bottom of the pull request. |
…s are not discared. In the sequential non-parallel path (ReadRecord->ReadAheadFromBuffer->ReadChunk) ReadChunk reads the whole chunk into memory. Most readers will round up the read to the blocksize and thereby prefetch some data from the next chunk. Currently ReadChunk recreates the reader each time and the previously prefetched data is lost and must be read again. Instead use get_backing_reader() directly each time. We can do this since ReadChunk is only called in single threaded context (Initialize, ReadRecord (parallelism disabled)) so there cannot be any concurrent access to the underlying reader. ReadTrace (before): ``` offset=64, size=1M <-- 1st chunk offset=1M, size=1M ... offset=8M, size=1M <-- block aligned read crosses chunk boundary offset=8.3M, size=0.7M <-- redundant read for 2nd chunk offset=9M, size=1M ... ``` ReadTrace (after): ``` offset=64, size=1M <-- 1st chunk offset=1M, size=1M ... offset=8M, size=1M <-- block aligned read crosses chunk boundary and is reused for the 2nd chunk offset=9M, size=1M ... ``` PiperOrigin-RevId: 577312179
copybara-service
bot
force-pushed
the
test_577312179
branch
from
fa16989 to
eea9f0d
Compare
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Reuse the same reader across ReadChunk calls so that prefetched blocks are not discared.
In the sequential non-parallel path (ReadRecord->ReadAheadFromBuffer->ReadChunk) ReadChunk reads the whole chunk into memory. Most readers will round up the read to the blocksize and thereby prefetch some data from the next chunk.
Currently ReadChunk recreates the reader each time and the previously prefetched data is lost and must be read again.
Instead use get_backing_reader() directly each time. We can do this since ReadChunk is only called in single threaded context (Initialize, ReadRecord (parallelism disabled)) so there cannot be any concurrent access to the underlying reader.
ReadTrace (before):
ReadTrace (after):