ensure BSFiles use blocks that are aligned to 512 Byte offsets

block-storage/src/main/java/org/lucares/pdb/diskstorage/DiskStorage.java

@@ -17,6 +17,7 @@ public class DiskStorage implements AutoCloseable {
 	private static final Logger LOGGER = LoggerFactory.getLogger(DiskStorage.class);
 
 	private static final long FREE_LIST_ROOT_OFFSET = 0;
+	private static final long NO_POINTER = 0;
 	private static final int FREE_LIST_NEXT_POINTER = 0;
 	private static final int FREE_LIST_PREV_POINTER = 8;
 	private static final int FREE_LIST_SIZE = 16;
@@ -31,11 +32,13 @@ public class DiskStorage implements AutoCloseable {
 		fileChannel = FileChannel.open(databaseFile, StandardOpenOption.READ, StandardOpenOption.WRITE,
 				StandardOpenOption.CREATE);
 
+		initIfNew();
+	}
+
+	private void initIfNew() throws IOException {
 		if (fileChannel.size() == 0) {
 			// file is new -> add root of the free list
-			// TODO implement a real free list
+			writeFreeListRootNodePosition(NO_POINTER);
-			final var src = ByteBuffer.allocate(8);
-			fileChannel.write(src, 0);
 		}
 	}
 
@@ -233,4 +236,14 @@ public class DiskStorage implements AutoCloseable {
 		freeListFirstBlock.putLong(0, freeListRootNodePosition);
 		fileChannel.write(freeListFirstBlock, FREE_LIST_ROOT_OFFSET);
 	}
+
+	public synchronized void ensureAlignmentForNewBlocks(final int alignment) throws IOException {
+		final long size = fileChannel.size();
+		final int alignmentMismatch = Math.floorMod(size, alignment);
+		if (alignmentMismatch != 0) {
+			// The next allocated block would not be aligned. Therefore we allocate a
+			// throw-away block.
+			allocateNewBlock(alignment - alignmentMismatch);
+		}
+	}
 }

data-store/src/main/java/org/lucares/pdb/datastore/internal/DataStore.java

@@ -66,6 +66,7 @@ public class DataStore implements AutoCloseable {
 		listingFilePath = storageBasePath.resolve("listing.csv");
 		diskStorageFilePath = storageBasePath.resolve("data.bs");
 		diskStorage = new DiskStorage(diskStorageFilePath);
+		diskStorage.ensureAlignmentForNewBlocks(BSFile.BLOCK_SIZE);
 		initListingFileIfNotExists();
 		init(diskStorage);
 		listingFile = new RandomAccessFile(listingFilePath.toFile(), "rw");

data-store/src/test/java/org/lucares/pdb/datastore/internal/DataStoreTest.java

@@ -9,6 +9,7 @@ import java.util.List;
 import java.util.Map;
 
 import org.lucares.pdb.api.Tags;
+import org.lucares.pdb.blockstorage.BSFile;
 import org.lucares.pdb.datastore.Doc;
 import org.lucares.utils.CollectionUtils;
 import org.lucares.utils.file.FileUtils;
@@ -106,6 +107,14 @@ public class DataStoreTest {
 		Assert.assertEquals(docsFlamingoJennifer.size(), 1, "doc for docsFlamingoJennifer");
 	}
 
+	public void testBlockAlignment() throws IOException {
+
+		dataStore = new DataStore(dataDirectory);
+		final Tags eagleTim = Tags.create("bird", "eagle", "name", "Tim");
+		final long eagleTimBlockOffset = dataStore.createNewFile(eagleTim);
+		Assert.assertEquals(eagleTimBlockOffset % BSFile.BLOCK_SIZE, 0);
+	}
+
 	private void assertSearch(final String query, final Tags... tags) {
 		final List<Doc> actualDocs = dataStore.search(query);
 		final List<Long> actual = CollectionUtils.map(actualDocs, Doc::getRootBlockNumber);