Add minor fixes in WarmDiskThresholdDecider (opensearch-project#18456)

Signed-off-by: Gagan Singh Saini <[email protected]>

Author: Gagan6164

server/src/main/java/org/opensearch/cluster/routing/allocation/decider/WarmDiskThresholdDecider.java

@@ -123,8 +123,8 @@ public Decision canAllocate(ShardRouting shardRouting, RoutingNode node, Routing
 
         final long totalAddressableSpace = calculateTotalAddressableSpace(node, allocation);
         final long currentNodeRemoteShardSize = calculateCurrentNodeRemoteShardSize(node, allocation, false);
-        final long freeSpace = totalAddressableSpace - currentNodeRemoteShardSize;
-        final long freeSpaceAfterAllocation = freeSpace > shardSize ? freeSpace - shardSize : 0;
+        final long freeSpace = Math.max(totalAddressableSpace - currentNodeRemoteShardSize, 0);
+        final long freeSpaceAfterAllocation = Math.max(freeSpace - shardSize, 0);
         final long freeSpaceLowThreshold = calculateFreeSpaceLowThreshold(diskThresholdSettings, totalAddressableSpace);
 
         final ByteSizeValue freeSpaceLowThresholdInByteSize = new ByteSizeValue(freeSpaceLowThreshold);
@@ -145,7 +145,7 @@ public Decision canAllocate(ShardRouting shardRouting, RoutingNode node, Routing
             return allocation.decision(
                 Decision.NO,
                 NAME,
-                "allocating the shard to this node will bring the node above the low watermark cluster setting [%s=%s] "
+                "allocating the shard to this node will bring the node above the low watermark cluster setting [%s] "
                     + "and cause it to have less than the minimum required [%s] of addressable remote free space (free: [%s], estimated remote shard size: [%s])",
                 CLUSTER_ROUTING_ALLOCATION_LOW_DISK_WATERMARK_SETTING.getKey(),
                 freeSpaceLowThresholdInByteSize,
@@ -183,7 +183,7 @@ public Decision canRemain(ShardRouting shardRouting, RoutingNode node, RoutingAl
 
         final long totalAddressableSpace = calculateTotalAddressableSpace(node, allocation);
         final long currentNodeRemoteShardSize = calculateCurrentNodeRemoteShardSize(node, allocation, true);
-        final long freeSpace = totalAddressableSpace - currentNodeRemoteShardSize;
+        final long freeSpace = Math.max(totalAddressableSpace - currentNodeRemoteShardSize, 0);
 
         final long freeSpaceHighThreshold = calculateFreeSpaceHighThreshold(diskThresholdSettings, totalAddressableSpace);
 
@@ -200,8 +200,8 @@ public Decision canRemain(ShardRouting shardRouting, RoutingNode node, RoutingAl
             return allocation.decision(
                 Decision.NO,
                 NAME,
-                "the shard cannot remain on this node because it is above the high watermark cluster setting [%s=%s] "
-                    + "and there is less than the required [%s%%] free remote addressable space on node, actual free: [%s%%]",
+                "the shard cannot remain on this node because it is above the high watermark cluster setting [%s] "
+                    + "and there is less than the required [%s] free remote addressable space on node, actual free: [%s]",
                 CLUSTER_ROUTING_ALLOCATION_HIGH_DISK_WATERMARK_SETTING.getKey(),
                 freeSpaceHighThresholdInByteSize,
                 freeSpaceInByteSize

server/src/test/java/org/opensearch/cluster/routing/allocation/decider/WarmDiskThresholdDeciderTests.java

@@ -175,8 +175,8 @@ public void testCanAllocateInSufficientFreeSpace() {
             .build();
 
         final Map<String, Long> shardSizes = new HashMap<>();
-        shardSizes.put("[test][0][p]", 4000L); // 5000 bytes
-        shardSizes.put("[test][0][r]", 4000L);
+        shardSizes.put("[test][0][p]", 5500L); // 5500 bytes shard size and total addressable space - 5000 bytes
+        shardSizes.put("[test][0][r]", 5500L);
         shardSizes.put("[test2][0][p]", 1000L); // 1000 bytes
         shardSizes.put("[test2][0][r]", 1000L);
 
@@ -354,8 +354,8 @@ public void testCanRemainInsufficientSpace() {
         WarmDiskThresholdDecider decider = new WarmDiskThresholdDecider(settings, clusterSettings);
 
         final Map<String, Long> shardSizes = new HashMap<>();
-        shardSizes.put("[test][0][p]", 4000L); // 4000 bytes
-        shardSizes.put("[test][0][r]", 4000L);
+        shardSizes.put("[test][0][p]", 5500L); // Shard size more than total addressable space - 5000 bytes
+        shardSizes.put("[test][0][r]", 5500L);
         shardSizes.put("[test2][0][p]", 1000L); // 1000 bytes
         shardSizes.put("[test2][0][r]", 1000L);