OK, I agree, if we encounter into exceptional path frequently, it means the broker is not healthy, this kind of `memory leak` is acceptable.
Thanks, Tao Jiuming On 2025/07/17 12:47:22 Yunze Xu wrote: > Hi all, > > I noticed there is a difference of opinion for whether to recycle > failed recyclable objects. [1][2][3] So I'd like to open the > discussion in the mail list. > > Netty recycler is an object pool to reduce GC pressure for frequently > created and discarded objects. If a recyclable object fails, e.g. when > an `OpAddEntry` encounters an unexpected exception, IMO, it's > reasonable not to recycle it. > > When a recyclable object is not recycled, it just won't be reused from > the object pool. The worst case is that the memory of the whole object > pool is exhausted. After that > > It's true that if such objects are not recycled, there will be a > "memory leak". However, the worst result is that the pool memory is > exhausted. In this case, it will fall back to allocating objects via > the `newObject` method with a dummy handle [4]. The implementation of > this method usually allocates memory from JVM. In such cases, the > recyclable object will eventually be garbage collected. > > It's actually not a memory leak. Recyclable objects usually have short > life timing, for example, an `OpAddEntry` object is created when > starting an asynchronous send and recycled after the send is done. The > object is never referenced by any other object, so even if it's > allocated from JVM, it will eventually be garbage collected. > > The benefit to skip recycling objects for failures is that for rare > cases, retaining the object could help diagnose issues that are hard > to reproduce. Still take `OpAddEntry` for example, if it encountered > an unexpected exception, recycling it could set all fields with null, > so it's hard to know which ledger it belongs to (and other useful > fields) from the heap dump. > > [1] https://github.com/apache/pulsar/pull/24515#discussion_r2212602435 > [2] https://github.com/apache/pulsar/pull/24522#discussion_r2210814071 > [3] https://github.com/apache/pulsar/pull/24522#discussion_r2213100905 > [4] > https://github.com/netty/netty/blob/ab2d2cf3ff3a6f055368405af7f6e9dd5b8d144e/common/src/main/java/io/netty/util/Recycler.java#L189 > > Thanks, > Yunze >
