CNDB-15526: Load TOC component before performing component discovery (#2028)

### What is the issue

TOCComponent performs component discovery before loading the TOC. This
can be detrimental to custom component loading and can be optimized to
try loading the TOC directly first before resorting to discovery.

### What does this PR fix and why was it fixed

Load the TOC component without discovery if possible
Also don't check for compression file existence when not necessary since it will open the file

Author: driftx

src/java/org/apache/cassandra/io/sstable/format/TOCComponent.java

@@ -114,18 +114,29 @@ public static Set<Component> loadOrCreate(Descriptor descriptor)
         {
             try
             {
-                SSTableWatcher.instance.discoverComponents(descriptor);
-                return TOCComponent.loadTOC(descriptor);
+                // Try loading TOC first without discovering components or checking file existence.
+                return TOCComponent.loadTOC(descriptor, false);
             }
             catch (FileNotFoundException | NoSuchFileException e)
             {
-                Set<Component> components = descriptor.discoverComponents();
-                if (components.isEmpty())
-                    return components; // sstable doesn't exist yet
+                SSTableWatcher.instance.discoverComponents(descriptor);
+
+                // Try loading TOC again after discovering components, still without existence checks
+                try
+                {
+                    return TOCComponent.loadTOC(descriptor, false);
+                }
+                catch (FileNotFoundException | NoSuchFileException e2)
+                {
+                    // Still no TOC, create it from discovered components
+                    Set<Component> components = descriptor.discoverComponents();
+                    if (components.isEmpty())
+                        return components; // sstable doesn't exist yet
 
-                components.add(Components.TOC);
-                TOCComponent.appendTOC(descriptor, components);
-                return components;
+                    components.add(Components.TOC);
+                    TOCComponent.appendTOC(descriptor, components);
+                    return components;
+                }
             }
         }
         catch (IOException e)

src/java/org/apache/cassandra/io/sstable/metadata/MetadataSerializer.java

@@ -348,8 +348,6 @@ private ICompressor getEncryptor(Descriptor desc, boolean writeTime)
         }
 
         File compressionFile = desc.fileFor(Components.COMPRESSION_INFO);
-        if (!compressionFile.exists())
-            return null;
 
         try
         {
@@ -364,10 +362,12 @@ private ICompressor getEncryptor(Descriptor desc, boolean writeTime)
                 return compressor.encryptionOnly();
             return null;
         }
-        catch (Exception e)
+        catch (Throwable t)
         {
-            // If we can't read the compression metadata, assume no encryption
-            logger.debug("Could not read compression metadata for {}: {}", desc, e.getMessage());
+            // If we can't read the compression metadata, assume no encryption.
+            // During flush, the compression file may not be accessible yet in some implementations
+            // causing FSReadError. Catch Throwable to handle both Exception and Error.
+            logger.debug("Could not read compression metadata for {}: {}", desc, t.getMessage());
             return null;
         }
     }