Clarify alignment field in store copy protocol

Rename the 'recordSize' to 'requiredElementAlignment' in the store copy protocol, to abstract ourselves from the fact that we occasionally copy over record stores with that code.
The code is mean to be generic, and is indeed used to copy over other files, such as indexes and logs, and an element alignment requirement is a generic term for what we want.

enterprise/com/src/main/java/org/neo4j/com/storecopy/StoreCopyClient.java

@@ -345,10 +345,10 @@ private StoreWriter decorateWithProgressIndicator( final StoreWriter actual )
 
             @Override
             public long write( String path, ReadableByteChannel data, ByteBuffer temporaryBuffer,
-                    boolean hasData, int recordSize ) throws IOException
+                    boolean hasData, int requiredElementAlignment ) throws IOException
             {
                 log.info( "Copying %s", path );
-                long written = actual.write( path, data, temporaryBuffer, hasData, recordSize );
+                long written = actual.write( path, data, temporaryBuffer, hasData, requiredElementAlignment );
                 log.info( "Copied %s %s", path, bytes( written ) );
                 totalFiles++;
                 return written;

enterprise/com/src/main/java/org/neo4j/com/storecopy/StoreWriter.java

@@ -26,11 +26,17 @@
 
 public interface StoreWriter extends Closeable
 {
-    // "hasData" is an effect of the block format not supporting a zero length block
-    // whereas a neostore file may actually be 0 bytes we'll have to keep track
-    // of that special case.
-    long write( String path, ReadableByteChannel data, ByteBuffer temporaryBuffer, boolean hasData, int recordSize )
-            throws IOException;
+    /**
+     * Pipe the data from the given {@link ReadableByteChannel} to a location given by the {@code path}, using the
+     * given {@code temporaryBuffer} for buffering if necessary.
+     * The {@code hasData} is an effect of the block format not supporting a zero length blocks, whereas a neostore
+     * file may actually be 0 bytes we'll have to keep track of that special case.
+     * The {@code requiredElementAlignment} parameter specifies the size in bytes to which the transferred elements
+     * should be aligned. For record store files, this is the record size. For files that have no special alignment
+     * requirements, you should use the value {@code 1} to signify that any alignment will do.
+     */
+    long write( String path, ReadableByteChannel data, ByteBuffer temporaryBuffer, boolean hasData,
+                int requiredElementAlignment ) throws IOException;
 
     @Override
     void close();

enterprise/com/src/main/java/org/neo4j/com/storecopy/ToFileStoreWriter.java

@@ -55,7 +55,7 @@ public ToFileStoreWriter( File graphDbStoreDir, StoreCopyClient.Monitor monitor,
 
     @Override
     public long write( String path, ReadableByteChannel data, ByteBuffer temporaryBuffer, boolean hasData,
-            int recordSize ) throws IOException
+            int requiredElementAlignment ) throws IOException
     {
         try
         {
@@ -73,7 +73,7 @@ public long write( String path, ReadableByteChannel data, ByteBuffer temporaryBu
                 // The reason is that we are copying to a temporary store location, and then we'll move the files later.
                 if ( storeType.isPresent() && storeType.get().isRecordStore() )
                 {
-                    int filePageSize = filePageSize( recordSize );
+                    int filePageSize = filePageSize( requiredElementAlignment );
                     try ( PagedFile pagedFile = pageCache.map( file, filePageSize, CREATE, WRITE ) )
                     {
                         final long written = writeDataThroughPageCache( pagedFile, data, temporaryBuffer, hasData );
@@ -102,11 +102,13 @@ private void addPageCacheMoveAction( File file )
                 pageCache.renameFile( file, new File( toDir, file.getName() ), copyOptions ) ) );
     }
 
-    private int filePageSize( int recordSize )
+    private int filePageSize( int alignment )
     {
+        // We know we are dealing with a record store at this point, so the required alignment is the record size,
+        // and we can use this to do the page size calculation in the same way as the stores would.
         final int pageCacheSize = pageCache.pageSize();
-        return (recordSize == NO_RECORD_SIZE) ? pageCacheSize
-                                              : (pageCacheSize - (pageCacheSize % recordSize));
+        return (alignment == NO_RECORD_SIZE) ? pageCacheSize
+                                              : (pageCacheSize - (pageCacheSize % alignment));
     }
 
     private long writeDataThroughFileSystem( File file, ReadableByteChannel data, ByteBuffer temporaryBuffer,

enterprise/com/src/main/java/org/neo4j/com/storecopy/ToNetworkStoreWriter.java

@@ -45,7 +45,7 @@ public ToNetworkStoreWriter( ChannelBuffer targetBuffer, Monitors monitors )
 
     @Override
     public long write( String path, ReadableByteChannel data, ByteBuffer temporaryBuffer,
-            boolean hasData, int recordSize ) throws IOException
+            boolean hasData, int requiredElementAlignment ) throws IOException
     {
         char[] chars = path.toCharArray();
         targetBuffer.writeShort( chars.length );
@@ -56,7 +56,7 @@ public long write( String path, ReadableByteChannel data, ByteBuffer temporaryBu
         long totalWritten = Short.BYTES + chars.length* Character.BYTES + Byte.BYTES;
         if ( hasData )
         {
-            targetBuffer.writeInt( recordSize );
+            targetBuffer.writeInt( requiredElementAlignment );
             totalWritten += Integer.BYTES;
             totalWritten += buffer.write( data );
             buffer.close();