guyinyou opened a new issue, #10035:
URL: https://github.com/apache/rocketmq/issues/10035
### Before Creating the Enhancement Request
- [x] I have confirmed that this should be classified as an enhancement
rather than a bug/feature.
### Summary
Fix the page alignment logic in DefaultMappedFile to avoid unnecessary
padding when the message end position is already page-aligned. Currently, when
endpos is exactly a multiple of UNSAFE_PAGE_SIZE, the calculation results in
extraAppendSize equal to UNSAFE_PAGE_SIZE, causing an entire page of
unnecessary padding.
### Motivation
When writing messages to mapped files, the system aligns the end position to
page boundaries for optimal memory-mapped I/O performance. However, there's a
boundary case where if the message end position (endpos) is already aligned to
UNSAFE_PAGE_SIZE, the current calculation `UNSAFE_PAGE_SIZE - endpos %
UNSAFE_PAGE_SIZE` results in UNSAFE_PAGE_SIZE instead of 0. This causes
unnecessary padding of an entire page size, wasting disk space and potentially
affecting write performance. This enhancement improves the efficiency of the
page alignment mechanism.
### Describe the Solution You'd Like
Add a boundary check after calculating extraAppendSize:
- If extraAppendSize equals UNSAFE_PAGE_SIZE (meaning endpos is already
page-aligned), set it to 0
- This ensures no unnecessary padding is added when the position is already
aligned
Implementation:
int extraAppendSize = UNSAFE_PAGE_SIZE - endpos % UNSAFE_PAGE_SIZE;
if (extraAppendSize == UNSAFE_PAGE_SIZE) {
extraAppendSize = 0;
}
### Describe Alternatives You've Considered
Using modulo operation differently: Could use (UNSAFE_PAGE_SIZE - endpos %
UNSAFE_PAGE_SIZE) % UNSAFE_PAGE_SIZE, but this is less readable and the
explicit check is clearer.
Pre-checking alignment: Check if endpos % UNSAFE_PAGE_SIZE == 0 before
calculation, but this requires an extra modulo operation and the current
solution is more efficient.
No change: Accept the current behavior, but this wastes disk space
unnecessarily and doesn't align with the optimization goals of the page
alignment mechanism.
### Additional Context
_No response_
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