GWphua opened a new pull request, #18687: URL: https://github.com/apache/druid/pull/18687
Fixes #18446 ### Description This PR belongs to a set of PR's that hope to optimize the start-up time of Historical. I came across this problem when I am running 100+ Historical servers, each needing to process a large number of segments during start-up (~85k). When conducting any updates to the Historical, each segment will take 15.3ms to load, and the start-up time for one historical will easily take >20mins. (Meaning 1.5 days to complete update for all Historical servers!) I looked to using `lazyLoadOnStart` to speed up startup time. Lazy loading processes each segment metadata in 3.23ms, and this shortens the start-up time to ~4min. However, using this strategy will cause some hiccups to query latency when we are trying to conduct an upgrade. I plan to solve this by selectively choosing which segments to load during Historical startup. <img width="1822" height="418" alt="image" src="https://github.com/user-attachments/assets/20c769b0-f464-4ed3-b66a-a942fc326f29"; /> #### Finding a middle ground By studying the usage pattern of my clusters, I noticed that each Historical stores 1 month worth of data, but the heavy querying is only restricted to 7 days, while occasional queries are issued for the time period out of the last 7 days. Hence, I changed the logic of segment loading during Historical startup to provide a configurable time period to load segments eagerly (and the rest lazily). The use of the time period is dependent on the querying habits of the cluster. Here's a benchmark of the improvements. I also included a test for #18489, which helps me to shave 10s off the start-up time. |Description | Loading Time| |-- | --| | Original v27 | 1,494.631 s | | EagerLoadingForPeriod | 328.819 s | | EagerLoadingForPeriod + ConcurrentSegmentFileLoad | 318.262 s | <!-- In each section, please describe design decisions made, including: - Choice of algorithms - Behavioral aspects. What configuration values are acceptable? How are corner cases and error conditions handled, such as when there are insufficient resources? - Class organization and design (how the logic is split between classes, inheritance, composition, design patterns) - Method organization and design (how the logic is split between methods, parameters and return types) - Naming (class, method, API, configuration, HTTP endpoint, names of emitted metrics) --> <!-- It's good to describe an alternative design (or mention an alternative name) for every design (or naming) decision point and compare the alternatives with the designs that you've implemented (or the names you've chosen) to highlight the advantages of the chosen designs and names. --> <!-- If there was a discussion of the design of the feature implemented in this PR elsewhere (e. g. a "Proposal" issue, any other issue, or a thread in the development mailing list), link to that discussion from this PR description and explain what have changed in your final design compared to your original proposal or the consensus version in the end of the discussion. If something hasn't changed since the original discussion, you can omit a detailed discussion of those aspects of the design here, perhaps apart from brief mentioning for the sake of readability of this PR description. --> <!-- Some of the aspects mentioned above may be omitted for simple and small changes. --> #### Release note <!-- Give your best effort to summarize your changes in a couple of sentences aimed toward Druid users. If your change doesn't have end user impact, you can skip this section. For tips about how to write a good release note, see [Release notes](https://github.com/apache/druid/blob/master/CONTRIBUTING.md#release-notes). --> Segment loading during Historical service startup is now configurable with `druid.segmentCache.startupLoadStrategy`. This new setting allows users to choose between the existing eager loading (loadAllEagerly), a new lazy loading (loadAllLazily) option for faster startups, and a hybrid strategy (loadEagerlyBeforePeriod) that ensures low query latency for the most recent data while deferring the loading cost of older data. <hr> ##### Key changed/added classes in this PR * `docs/configuration/index.md` * `SegmentStatsMonitor` * `SegmentLoaderConfig` * `SegmentLocalCacheManager` * `startup/HistoricalStartupCacheLoadStrategy` * `startup/HistoricalStartupCacheLoadStrategyFactory` * `startup/LoadAllEagerlyStrategy` * `startup/LoadAllLazilyStrategy` * `startup/LoadEagerlyBeforePeriod` <hr> <!-- Check the items by putting "x" in the brackets for the done things. Not all of these items apply to every PR. Remove the items which are not done or not relevant to the PR. None of the items from the checklist below are strictly necessary, but it would be very helpful if you at least self-review the PR. --> This PR has: - [x] been self-reviewed. - [x] added documentation for new or modified features or behaviors. - [x] a release note entry in the PR description. - [x] added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links. - [x] added or updated version, license, or notice information in [licenses.yaml](https://github.com/apache/druid/blob/master/dev/license.md) - [x] 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. - [x] been tested in a test Druid cluster. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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