Prevent write timeouts due to lock contention in WAL #3886
Merged
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
|
Seems reasonable. |
| partitionsToWrite := l.pointsToPartitions(points) | ||
| l.mu.RUnlock() |
There was a problem hiding this comment.
Any point adding a comment.....// persist the raw point data, holding the lock for as short as possible.
I am a little concerned future developers would revert to defer. We're adding some important changes, but it may not be obvious why in the future.
|
Probably worthy of a CHANELOG addition, mentioning it reduces the number of timeouts during writes, so the community knows there is a reason for improvements they might see (and that they are not imagining it). |
The log was deferring the release of the read lock on the WAL. This had the affect that a read-lock was held until after the partition finished writing (which maintains it's own locks). The read lock is only needed around the call to pointsToPartions so it can get a consistent copy of the points to write. After that calls returns, a lock is not needed so free it immediatedly.
A write lock was being taken to read the memory size to determine if writes should be paused. What happens is that writers get blocked indefintely when trying to acquire a write lock which makes writes pause (or stop) for long periods of time.
|
+1 |
jwilder
added a commit
that referenced
this pull request
Aug 28, 2015
Prevent write timeouts due to lock contention in WAL
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Outdated suggestions cannot be applied.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.
When disk operations slow down or the amount of work required to flush writes to the index takes too long, the lock contention on the WAL can cause timeouts for writes. The PR reduces some the contention for some of the locks when these timeouts occur and prevents write timeouts in scenarios.