[CASSANDRA-15396] RandomAccessReader does not override skip or skipBytes so will do a lot of disk io when n is large

• Type: Improvement
• Status: Review In Progress
• Priority: Normal
• Resolution: Unresolved
• Component/s: Local/SSTable
• Change Category: Performance
• Complexity: Low Hanging Fruit
• Platform: All

Test and Documentation Plan

PR	tests
link	link

In my testing, the following cases improve by relying on seek:

1) compressed data (avoid decompressing when not needed)
2) non-mmap data (avoid the extra extra io)

The cases which did not improve noticeably (but also did not regress):

1) mmap data which is in the page cache (mmap rebuffer doesn’t copy into buffers, instead switches the position of the buffer. This patch lowers the amount of times we update the buffer position)

Plan to run stress tests as well, but still learning the Data.db read path to figure out which patterns call .skipByte*

• Assignee: David Capwell
• Reporter: David Capwell

Authors

David Capwell

Reviewers

Dinesh Joshi

• Created: 01/Nov/19 17:23
• Updated: 05/May/20 17:30

Description

RandomAccessReader does not override skip or skipBytes which becomes a problem when the size of n (the bytes to skip) is larger than a single buffer; in these cases we can rely on seek to avoid the extra disk io.