Zarr bug fix and improvements

cdm/zarr/src/main/java/ucar/nc2/iosp/zarr/ZarrHeader.java

@@ -54,6 +54,7 @@ private class DelayedVarMaker {
     private RandomAccessDirectoryItem var;
     private ZArray zarray;
     private Map<Integer, Long> initializedChunks; // track any uninitialized chunks for var
+    private Map<Integer, Long> chunkStarts; // byte offset of each chunk within the store, keyed by chunk index
     private List<Attribute> attrs; // list of variable attributes
     private long dataOffset; // byte position where data starts
 
@@ -65,6 +66,7 @@ void setVar(RandomAccessDirectoryItem var) {
       this.var = var;
       this.attrs = null;
       this.initializedChunks = new HashMap<>();
+      this.chunkStarts = new HashMap<>();
       this.dataOffset = -1;
       if (var != null) {
         try {
@@ -104,6 +106,11 @@ void processItem(RandomAccessDirectoryItem item) {
         this.var = null; // skip rest of var is unrecognized files found
       }
       this.initializedChunks.put(index, item.length());
+      // Record the actual byte offset of this chunk within the store, keyed by its numeric chunk index.
+      // This avoids any dependency on the order in which the store lists files (which is lexicographic
+      // and would otherwise place e.g. chunk 0.10 before chunk 0.2, which is the root cause of
+      // https://github.com/Unidata/netcdf-java/issues/1542)
+      this.chunkStarts.put(index, item.startIndex());
       // if data offset is uninitialized, set here
       if (this.dataOffset < 0) {
         this.dataOffset = item.startIndex();
@@ -115,7 +122,7 @@ void makeVar() {
         return; // do nothing if no variable is in progress
       }
       try {
-        makeVariable(var, dataOffset, zarray, initializedChunks, attrs);
+        makeVariable(var, dataOffset, zarray, initializedChunks, chunkStarts, attrs);
       } catch (ZarrFormatException ex) {
         logger.error(ex.getMessage());
       }
@@ -200,7 +207,8 @@ private void makeGroup(RandomAccessDirectoryItem item, List<Attribute> attrs) {
   }
 
   private void makeVariable(RandomAccessDirectoryItem item, long dataOffset, ZArray zarray,
-      Map<Integer, Long> initializedChunks, List<Attribute> attrs) throws ZarrFormatException {
+      Map<Integer, Long> initializedChunks, Map<Integer, Long> chunkStarts, List<Attribute> attrs)
+      throws ZarrFormatException {
     // make new Variable
     Variable.Builder<?> var = Variable.builder();
     String location = ZarrUtils.trimLocation(item.getLocation());
@@ -303,7 +311,7 @@ private void makeVariable(RandomAccessDirectoryItem item, long dataOffset, ZArra
 
     // create VInfo
     VInfo vinfo = new VInfo(chunks, zarray.getFillValue(), zarray.getCompressor(), zarray.getByteOrder(),
-        zarray.getOrder(), zarray.getSeparator(), zarray.getFilters(), dataOffset, initializedChunks,
+        zarray.getOrder(), zarray.getSeparator(), zarray.getFilters(), dataOffset, initializedChunks, chunkStarts,
         zarray.getElementSize(), zarray.isUnicodeString());
     var.setSPobject(vinfo);
 
@@ -389,7 +397,7 @@ private static int getChunkIndex(RandomAccessDirectoryItem item, ZArray zarray)
       int[] shape = zarray.getShape();
       int[] chunkSize = zarray.getChunks();
       for (int i = 0; i < nDims; i++) {
-        nChunks[i] = (int) Math.ceil(shape[i] / chunkSize[i]);
+        nChunks[i] = (int) Math.ceil((double) shape[i] / chunkSize[i]);
       }
       return ZarrUtils.subscriptsToIndex(subs, nChunks);
     } else {
@@ -422,12 +430,13 @@ class VInfo {
     private final List<Filter> filters;
     private final long offset;
     private final Map<Integer, Long> initializedChunks;
+    private final Map<Integer, Long> chunkStarts;
     private final int elementSize;
     private final boolean unicodeString;
 
     VInfo(int[] chunks, Object fillValue, Filter compressor, ByteOrder byteOrder, ZArray.Order order, String separator,
-        List<Filter> filters, long offset, Map<Integer, Long> initializedChunks, int elementSize,
-        boolean unicodeString) {
+        List<Filter> filters, long offset, Map<Integer, Long> initializedChunks, Map<Integer, Long> chunkStarts,
+        int elementSize, boolean unicodeString) {
       this.chunks = chunks;
       this.fillValue = fillValue;
       this.byteOrder = byteOrder;
@@ -437,6 +446,7 @@ class VInfo {
       this.filters = filters;
       this.offset = offset;
       this.initializedChunks = initializedChunks;
+      this.chunkStarts = chunkStarts;
       this.elementSize = elementSize;
       this.unicodeString = unicodeString;
     }
@@ -477,6 +487,10 @@ public Map<Integer, Long> getInitializedChunks() {
       return this.initializedChunks;
     }
 
+    public Map<Integer, Long> getChunkStarts() {
+      return this.chunkStarts;
+    }
+
     int getElementSize() {
       return this.elementSize;
     }

cdm/zarr/src/main/java/ucar/nc2/iosp/zarr/ZarrLayoutBB.java

@@ -38,6 +38,7 @@ public class ZarrLayoutBB implements LayoutBB {
   private int totalNChunks; // total number of chunks
   private boolean F_order = false; // F order storage?
   private Map<Integer, Long> initializedChunks; // set of chunks that exist as files and their compressed size
+  private Map<Integer, Long> chunkStarts; // byte offset of each existing chunk within the store, keyed by chunk index
   private Filter compressor;
   private List<Filter> filters;
 
@@ -55,12 +56,13 @@ public ZarrLayoutBB(Variable v2, Section wantSection, RandomAccessFile raf) {
     this.chunkSize = vinfo.getChunks();
     int ndims = this.chunkSize.length;
     this.initializedChunks = vinfo.getInitializedChunks();
+    this.chunkStarts = vinfo.getChunkStarts();
     this.nChunks = new int[ndims];
     this.totalNChunks = 1;
     for (int i = 0; i < ndims; i++) {
       Dimension dim = v2.getDimension(i);
       // round up nchunks if not evenly divisible by chunk size
-      this.nChunks[i] = (int) Math.ceil(dim.getLength() / this.chunkSize[i]);
+      this.nChunks[i] = (int) Math.ceil((double) dim.getLength() / this.chunkSize[i]);
       this.totalNChunks *= nChunks[i];
     }
 
@@ -120,15 +122,16 @@ private class DataChunkIterator implements LayoutBBTiled.DataChunkIterator {
     DataChunkIterator() {
       this.currChunk = new int[chunkSize.length];
       this.chunkNum = 0;
-      this.currOffset = varOffset; // start at start of variable data
+      this.currOffset = chunkStarts.getOrDefault(this.chunkNum, varOffset);
     }
 
     public boolean hasNext() {
       return this.chunkNum < totalNChunks;
     }
 
     public LayoutBBTiled.DataChunk next() {
-      DataChunk chunk = new ZarrLayoutBB.DataChunk(this.currChunk, this.chunkNum, this.currOffset);
+      long offset = chunkStarts.getOrDefault(this.chunkNum, this.currOffset);
+      DataChunk chunk = new ZarrLayoutBB.DataChunk(this.currChunk, this.chunkNum, offset);
       incrementChunk();
       return chunk;
     }
@@ -142,7 +145,6 @@ private void incrementChunk() {
           i--;
         }
         this.currChunk[i]++;
-        this.currOffset += initializedChunks.getOrDefault(this.chunkNum, (long) 0);
         this.chunkNum = ZarrUtils.subscriptsToIndex(this.currChunk, nChunks);
       } else {
         // scalar array

cdm/zarr/src/test/data/scripts/zarr_o10_multichunk.py

@@ -0,0 +1,25 @@
+import numpy as np
+import zarr
+
+store = zarr.storage.LocalStore('../test_o10_multichunk.zarr')
+
+# create array
+data = np.arange(10000).reshape((100,100))
+
+root_group = zarr.group(store, overwrite=True, zarr_format=2)
+
+# create array with more than 10 chunks in each dimension
+# 10 chunks in first dimension, 20 chunks in second
+# so chunks will be [0-9].[0-19]
+multichunk = root_group.create_array('ten_by_five', shape=data.shape, chunks=(10,5), dtype='<u8', overwrite=True, compressors=None)
+multichunk[:] = data
+
+multichunk_blosc = root_group.create_array('ten_by_five_blosc', shape=data.shape, chunks=(10,5), dtype='<u8', overwrite=True)
+multichunk_blosc[:] = data
+
+compressors=None
+print(multichunk)
+print(multichunk[:])
+
+print(multichunk_blosc)
+print(multichunk_blosc[:])

cdm/zarr/src/test/data/test_o10_multichunk.zarr/.zattrs

@@ -0,0 +1 @@
+{}

cdm/zarr/src/test/data/test_o10_multichunk.zarr/.zgroup

@@ -0,0 +1,3 @@
+{
+  "zarr_format": 2
+}

cdm/zarr/src/test/data/test_o10_multichunk.zarr/ten_by_five/.zarray

@@ -0,0 +1,17 @@
+{
+  "shape": [
+    100,
+    100
+  ],
+  "chunks": [
+    10,
+    5
+  ],
+  "dtype": "<u8",
+  "fill_value": 0,
+  "order": "C",
+  "filters": null,
+  "dimension_separator": ".",
+  "compressor": null,
+  "zarr_format": 2
+}

cdm/zarr/src/test/data/test_o10_multichunk.zarr/ten_by_five/.zattrs

@@ -0,0 +1 @@
+{}

cdm/zarr/src/test/data/test_o10_multichunk.zarr/ten_by_five_blosc/.zarray

@@ -0,0 +1,23 @@
+{
+  "shape": [
+    100,
+    100
+  ],
+  "chunks": [
+    10,
+    5
+  ],
+  "dtype": "<u8",
+  "fill_value": 0,
+  "order": "C",
+  "filters": null,
+  "dimension_separator": ".",
+  "compressor": {
+    "id": "blosc",
+    "cname": "lz4",
+    "clevel": 5,
+    "shuffle": 1,
+    "blocksize": 0
+  },
+  "zarr_format": 2
+}

cdm/zarr/src/test/data/test_o10_multichunk.zarr/ten_by_five_blosc/.zattrs

@@ -0,0 +1 @@
+{}