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Posted to commits@druid.apache.org by GitBox <gi...@apache.org> on 2022/10/12 19:45:23 UTC
[GitHub] [druid] zachjsh opened a new pull request, #13219: Improve global-cached-lookups metric reporting
zachjsh opened a new pull request, #13219:
URL: https://github.com/apache/druid/pull/13219
It was found that the `namespace/cache/heapSizeInBytes` metric that tracks the total heap size in bytes of all lookup caches loaded on a service instance was being under reported. We were not accounting for the memory overhead of the String object, which I've found in testing to be ~40 bytes. While this overhead may be java version dependent, it should not vary much, and accounting for this provides a better estimate. Also fixed some logging, and reading bytes from the JDBI result set a little more efficient by saving hash table lookups.
This PR has:
- [x] been self-reviewed.
- [ ] using the [concurrency checklist](https://github.com/apache/druid/blob/master/dev/code-review/concurrency.md) (Remove this item if the PR doesn't have any relation to concurrency.)
- [ ] added documentation for new or modified features or behaviors.
- [ ] a release note entry in the PR description.
- [ ] added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
- [ ] added or updated version, license, or notice information in [licenses.yaml](https://github.com/apache/druid/blob/master/dev/license.md)
- [ ] added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
- [ ] added unit tests or modified existing tests to cover new code paths, ensuring the threshold for [code coverage](https://github.com/apache/druid/blob/master/dev/code-review/code-coverage.md) is met.
- [ ] added integration tests.
- [ ] been tested in a test Druid cluster.
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[GitHub] [druid] kfaraz commented on a diff in pull request #13219: Improve global-cached-lookups metric reporting
Posted by GitBox <gi...@apache.org>.
kfaraz commented on code in PR #13219:
URL: https://github.com/apache/druid/pull/13219#discussion_r994041387
##########
extensions-core/lookups-cached-global/src/main/java/org/apache/druid/data/input/MapPopulator.java:
##########
@@ -245,7 +245,8 @@ static long getByteLengthOfObject(@Nullable Object o)
{
if (null != o) {
if (o.getClass().getName().equals(STRING_CLASS_NAME)) {
- return ((String) (o)).length();
+ // Each String object has ~40 bytes of overhead
+ return ((long) ((String) (o)).length() * Character.BYTES) + 40;
Review Comment:
You could also consider doing this instead:
https://github.com/apache/druid/blob/master/processing/src/main/java/org/apache/druid/segment/StringDimensionDictionary.java#L41-L47
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[GitHub] [druid] abhishekagarwal87 commented on a diff in pull request #13219: Improve global-cached-lookups metric reporting
Posted by GitBox <gi...@apache.org>.
abhishekagarwal87 commented on code in PR #13219:
URL: https://github.com/apache/druid/pull/13219#discussion_r994291902
##########
extensions-core/lookups-cached-global/src/main/java/org/apache/druid/data/input/MapPopulator.java:
##########
@@ -245,7 +245,8 @@ static long getByteLengthOfObject(@Nullable Object o)
{
if (null != o) {
if (o.getClass().getName().equals(STRING_CLASS_NAME)) {
- return ((String) (o)).length();
+ // Each String object has ~40 bytes of overhead
+ return ((long) ((String) (o)).length() * Character.BYTES) + 40;
Review Comment:
it's better to use the same calculation and code.
@zachjsh - can you reuse the code? The common code can be placed in `StringUtils` class.
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[GitHub] [druid] kfaraz commented on a diff in pull request #13219: Improve global-cached-lookups metric reporting
Posted by GitBox <gi...@apache.org>.
kfaraz commented on code in PR #13219:
URL: https://github.com/apache/druid/pull/13219#discussion_r994041387
##########
extensions-core/lookups-cached-global/src/main/java/org/apache/druid/data/input/MapPopulator.java:
##########
@@ -245,7 +245,8 @@ static long getByteLengthOfObject(@Nullable Object o)
{
if (null != o) {
if (o.getClass().getName().equals(STRING_CLASS_NAME)) {
- return ((String) (o)).length();
+ // Each String object has ~40 bytes of overhead
+ return ((long) ((String) (o)).length() * Character.BYTES) + 40;
Review Comment:
You could also consider doing this instead:
https://github.com/apache/druid/blob/346fbf133fa338fe0ccf76b5537eb1627f28a487/processing/src/main/java/org/apache/druid/segment/StringDimensionDictionary.java#L42
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[GitHub] [druid] kfaraz commented on a diff in pull request #13219: Improve global-cached-lookups metric reporting
Posted by GitBox <gi...@apache.org>.
kfaraz commented on code in PR #13219:
URL: https://github.com/apache/druid/pull/13219#discussion_r994278022
##########
extensions-core/lookups-cached-global/src/main/java/org/apache/druid/data/input/MapPopulator.java:
##########
@@ -245,7 +245,8 @@ static long getByteLengthOfObject(@Nullable Object o)
{
if (null != o) {
if (o.getClass().getName().equals(STRING_CLASS_NAME)) {
- return ((String) (o)).length();
+ // Each String object has ~40 bytes of overhead
+ return ((long) ((String) (o)).length() * Character.BYTES) + 40;
Review Comment:
I think we can proceed with what you have. It's a difference of just 4 bytes (40 vs 44) per String anyway, and as you mention, it does depend on java version.
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[GitHub] [druid] kfaraz commented on a diff in pull request #13219: Improve global-cached-lookups metric reporting
Posted by GitBox <gi...@apache.org>.
kfaraz commented on code in PR #13219:
URL: https://github.com/apache/druid/pull/13219#discussion_r994041387
##########
extensions-core/lookups-cached-global/src/main/java/org/apache/druid/data/input/MapPopulator.java:
##########
@@ -245,7 +245,8 @@ static long getByteLengthOfObject(@Nullable Object o)
{
if (null != o) {
if (o.getClass().getName().equals(STRING_CLASS_NAME)) {
- return ((String) (o)).length();
+ // Each String object has ~40 bytes of overhead
+ return ((long) ((String) (o)).length() * Character.BYTES) + 40;
Review Comment:
You could also consider doing this instead:
https://github.com/apache/druid/blob/346fbf133fa338fe0ccf76b5537eb1627f28a487/processing/src/main/java/org/apache/druid/segment/StringDimensionDictionary.java#L41-L47
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[GitHub] [druid] zachjsh merged pull request #13219: Improve global-cached-lookups metric reporting
Posted by GitBox <gi...@apache.org>.
zachjsh merged PR #13219:
URL: https://github.com/apache/druid/pull/13219
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[GitHub] [druid] zachjsh commented on a diff in pull request #13219: Improve global-cached-lookups metric reporting
Posted by GitBox <gi...@apache.org>.
zachjsh commented on code in PR #13219:
URL: https://github.com/apache/druid/pull/13219#discussion_r994245240
##########
extensions-core/lookups-cached-global/src/main/java/org/apache/druid/data/input/MapPopulator.java:
##########
@@ -245,7 +245,8 @@ static long getByteLengthOfObject(@Nullable Object o)
{
if (null != o) {
if (o.getClass().getName().equals(STRING_CLASS_NAME)) {
- return ((String) (o)).length();
+ // Each String object has ~40 bytes of overhead
+ return ((long) ((String) (o)).length() * Character.BYTES) + 40;
Review Comment:
Thanks for pointing this out! The I think depends on the particular version of java and beyond that the particular distribution of it. In my testing I found 40 bytes to be a good estimate for overhead. Sometimes I find that its a bit less. Will leave as is unless you feel strongly about changing.
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