GWphua commented on code in PR #18687:
URL: https://github.com/apache/druid/pull/18687#discussion_r2464294282
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docs/configuration/index.md:
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@@ -1602,6 +1604,14 @@ In `druid.segmentCache.locationSelector.strategy`, one
of `leastBytesUsed`, `rou
Note that if `druid.segmentCache.numLoadingThreads` > 1, multiple threads can
download different segments at the same time. In this case, with the
`leastBytesUsed` strategy or `mostAvailableSize` strategy, Historicals may
select a sub-optimal storage location because each decision is based on a
snapshot of the storage location status of when a segment is requested to
download.
+In `druid.segmentCache.startupLoadStrategy`, one of `loadAllEagerly`,
`loadAllLazily`, or `loadEagerlyBeforePeriod` could be specified to represent
the strategy to load segments when starting the Historical service.
+
+|Strategy|Description|
+|--------|-----------|
+|`loadAllEagerly`|The default startup strategy. The Historical service will
load all segment column metadata immediately during the initial startup
process.|
+|`loadAllLazily`|To significantly improve historical system startup time,
segments are not loaded during the initial startup sequence. Instead, the
loading cost is deferred, and will be incurred the first time a segment is
referenced by a query.|
+|`loadEagerlyBeforePeriod`|Provides a balance between fast startup and query
performance. The Historical service will eagerly load column metadata only for
segments that fall within the most recent period defined by
`druid.segmentCache.startupLoadPeriod`. Segments outside this recent period
will be loaded on-demand when first queried.|
Review Comment:
This is workable --
I can change `startupLoadStrategy.period` to
`startupLoadStrategy.datasourceToPeriodMapping`, which receives something like
a JSON
e.g.
`{"DS1": "P7D", "DS2": "P2D", "default": "P7D"}`
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