horizonzy commented on PR #21096:
URL: https://github.com/apache/pulsar/pull/21096#issuecomment-1704590008
> ```java
>
> ```
> I would like to provide another approach for handling the cached rack
configuration update.
>
> 1. Make allGroupsBookieMapping as a `volatile` variable
> 2. Update the cached rack configuration async
>
> initialize
>
> ```java
>
bookieMappingCache.get(BookieRackAffinityMapping.BOOKIE_INFO_ROOT_PATH).thenAccept(opt
-> {
> opt.ifPresent(bookiesRackConfiguration ->
cachedRackConfiguration = bookiesRackConfiguration);
> }).exceptionally(ex -> {
> log.warn("Failed to load bookies rack configuration while
initialize the PlacementPolicy.");
> return null;
> });
> ```
>
> getExcludedBookiesWithIsolationGroups
>
> ```java
> CompletableFuture<Optional<BookiesRackConfiguration>>
future =
>
bookieMappingCache.get(BookieRackAffinityMapping.BOOKIE_INFO_ROOT_PATH);
>
> BookiesRackConfiguration allGroupsBookieMapping;
> future.thenAccept(opt ->
> opt.ifPresent(bookiesRackConfiguration ->
cachedRackConfiguration = bookiesRackConfiguration)
> ).exceptionally(ex -> {
> log.warn("The newest bookie rack config is not
available now.");
> return null;
> });
> allGroupsBookieMapping = cachedRackConfiguration;
> if (allGroupsBookieMapping == null) {
> return excludedBookies;
> }
> ```
>
> When the broker restarts, we might lose the rack configurations, but it
can avoid any potential deadlocks.
>
> The initialize method is called when starting the broker before the broker
service becomes available to the client. So we will not lose the bookie rack
configuration in most cases.
It makes sense, we should print a debug log when the allGroupsBookieMapping
is null.
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