junegunn commented on code in PR #7076:
URL: https://github.com/apache/hbase/pull/7076#discussion_r2134900857
##########
hbase-common/src/main/java/org/apache/hadoop/hbase/HConstants.java:
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@@ -1040,10 +1040,21 @@ public enum OperationStatusCode {
public static final String HFILE_PREAD_ALL_BYTES_ENABLED_KEY =
"hfile.pread.all.bytes.enabled";
public static final boolean HFILE_PREAD_ALL_BYTES_ENABLED_DEFAULT = false;
- /*
- * Minimum percentage of free heap necessary for a successful cluster
startup.
+ /**
+ * Configuration key for the minimum fraction of heap memory that must
remain free for a
+ * RegionServer to start
+ */
+ public static final String HBASE_REGION_SERVER_FREE_HEAP_MIN_SIZE_KEY =
+ "hbase.regionserver.free.heap.min.size";
+
+ public static final float HBASE_REGION_SERVER_FREE_HEAP_MIN_SIZE_DEFAULT =
0.1f;
+
+ /**
+ * Configuration key for the absolute amount of heap memory that must remain
free for a
+ * RegionServer to start
*/
- public static final float HBASE_CLUSTER_MINIMUM_MEMORY_THRESHOLD = 0.2f;
+ public static final String HBASE_REGION_SERVER_FREE_HEAP_MEMORY_MIN_SIZE_KEY
=
+ "hbase.regionserver.free.heap.memory.min.size";
Review Comment:
> Using an absolute size is not only more explicit for users, but also
provides more stability.
Thanks for giving my suggestion some thought. Considering the use cases and
requirements, I think it's enough to offer a single parameter for setting the
minimum amount of heap that should be left unreserved. Anyone who wants to
bypass the check can set it to 0, and those who want to have some safety
guarantee can set it to some realistic value. I believe it covers all
scenarios, and having another option might distract/confuse the users.
But that's just one perspective, and I hope to hear what others think as
well.
> If we go with absolute size only, we still need to think about the default
value.
Yeah, it's important to provide sensible defaults, but we should be extra
careful when changing the existing ones. Following "the principal of least
surprise", I would just leave the value undefined, which means that 20% of the
heap is used as the threshold as before.
> I'm also considering allowing this value to be disabled (by setting it to
0)
We should still allow `0` as a valid value for the option, for users who
want to bypass the check entirely. An empty value or a negative value can be
used instead to indicate an undefined state.
> overridden to something like 128m in
[conf/hbase-site.xml](https://github.com/apache/hbase/blob/master/conf/hbase-site.xml),
especially for test environments.
While I think it's reasonable, I'm not confident that it won't impact
existing user setups. In pseudo-distributed environments, users often run many
processes locally, each with a relatively small heap (e.g., 512MB). In such
cases, even 128m could cause their setup to stop working.
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