GWphua commented on issue #18446:
URL: https://github.com/apache/druid/issues/18446#issuecomment-3358942249
Hi @clintropolis, I have looked through #18176, and understand the
operations of segment cache loading as such. Correct me if I am wrong:
1. Coordinator assigns segments S1, S2, S3 to Historical H.
- Under normal mode: H would download S1, S2, S3 immediately, store on disk.
- Under virtual storage mode: H does *not* fetch them yet.
2. When a query arrives needing S2, S3:
Historical checks its cache:
- S2: not loaded → issue mount as weak entry
- S3: not loaded → issue mount
Once loaded, execute the query against them.
3. Later, more queries come requiring new segments S4:
If disk space is nearing limit: Weak entries evicted according to SIEVE
algorithm to make room, new requests mounted.
4. If a later query again needs S2:
If S2 was evicted, it will be loaded again
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