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Subject [GitHub] [drill] amansinha100 commented on a change in pull request #1738: DRILL-7062: Initial implementation of run-time row-group pruning
Date Mon, 08 Apr 2019 06:25:39 GMT
amansinha100 commented on a change in pull request #1738: DRILL-7062: Initial implementation
of run-time row-group pruning
URL: https://github.com/apache/drill/pull/1738#discussion_r272898010
 
 

 ##########
 File path: exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/AbstractParquetScanBatchCreator.java
 ##########
 @@ -68,76 +83,131 @@ protected ScanBatch getBatch(ExecutorFragmentContext context, AbstractParquetRow
     List<RecordReader> readers = new LinkedList<>();
     List<Map<String, String>> implicitColumns = new ArrayList<>();
     Map<String, String> mapWithMaxColumns = new LinkedHashMap<>();
-    for (RowGroupReadEntry rowGroup : rowGroupScan.getRowGroupReadEntries()) {
-      /*
-      Here we could store a map from file names to footers, to prevent re-reading the footer
for each row group in a file
-      TODO - to prevent reading the footer again in the parquet record reader (it is read
earlier in the ParquetStorageEngine)
-      we should add more information to the RowGroupInfo that will be populated upon the
first read to
-      provide the reader with all of th file meta-data it needs
-      These fields will be added to the constructor below
-      */
-      try {
-        Stopwatch timer = logger.isTraceEnabled() ? Stopwatch.createUnstarted() : null;
-        DrillFileSystem fs = fsManager.get(rowGroupScan.getFsConf(rowGroup), rowGroup.getPath());
-        ParquetReaderConfig readerConfig = rowGroupScan.getReaderConfig();
-        if (!footers.containsKey(rowGroup.getPath())) {
-          if (timer != null) {
-            timer.start();
+    ParquetReaderConfig readerConfig = rowGroupScan.getReaderConfig();
+    RowGroupReadEntry firstRowGroup = null; // to be scanned in case ALL row groups are pruned
out
+    ParquetMetadata firstFooter = null;
+    long rowgroupsPruned = 0; // for stats
+
+    try {
+
+      LogicalExpression filterExpr = rowGroupScan.getFilter();
+      Path selectionRoot = rowGroupScan.getSelectionRoot();
+      // Runtime pruning: Avoid recomputing metadata objects for each row-group in case they
use the same file
+      // by keeping the following objects computed earlier (relies on same file being in
consecutive rowgroups)
+      Path prevRowGroupPath = null;
+      Metadata_V3.ParquetTableMetadata_v3 tableMetadataV3 = null;
+      Metadata_V3.ParquetFileMetadata_v3 fileMetadataV3 = null;
+      FileSelection fileSelection = null;
+      ParquetTableMetadataProviderImpl metadataProvider = null;
+
+      for (RowGroupReadEntry rowGroup : rowGroupScan.getRowGroupReadEntries()) {
+        /*
+        Here we could store a map from file names to footers, to prevent re-reading the footer
for each row group in a file
+        TODO - to prevent reading the footer again in the parquet record reader (it is read
earlier in the ParquetStorageEngine)
+        we should add more information to the RowGroupInfo that will be populated upon the
first read to
+        provide the reader with all of th file meta-data it needs
+        These fields will be added to the constructor below
+        */
+
+          Stopwatch timer = logger.isTraceEnabled() ? Stopwatch.createUnstarted() : null;
+          DrillFileSystem fs = fsManager.get(rowGroupScan.getFsConf(rowGroup), rowGroup.getPath());
+          if (!footers.containsKey(rowGroup.getPath())) {
+            if (timer != null) {
+              timer.start();
+            }
+
+            ParquetMetadata footer = readFooter(fs.getConf(), rowGroup.getPath(), readerConfig);
+            if (timer != null) {
+              long timeToRead = timer.elapsed(TimeUnit.MICROSECONDS);
+              logger.trace("ParquetTrace,Read Footer,{},{},{},{},{},{},{}", "", rowGroup.getPath(),
"", 0, 0, 0, timeToRead);
+            }
+            footers.put(rowGroup.getPath(), footer);
           }
+          ParquetMetadata footer = footers.get(rowGroup.getPath());
+
+          //
+          //   If a filter is given (and it is not just "TRUE") - then use it to perform
run-time pruning
+          //
+          if ( filterExpr != null && ! (filterExpr instanceof ValueExpressions.BooleanExpression)
 ) { // skip when no filter or filter is TRUE
+
+            int rowGroupIndex = rowGroup.getRowGroupIndex();
+            long footerRowCount = footer.getBlocks().get(rowGroupIndex).getRowCount();
+
+            if ( timer != null ) {  // restart the timer, if tracing
+              timer.reset();
+              timer.start();
+            }
+
+            // When starting a new file, or at the first time - Initialize path specific
metadata etc
+            if ( ! rowGroup.getPath().equals(prevRowGroupPath) ) {
+              // Get the table metadata (V3)
+              tableMetadataV3 = Metadata.getParquetTableMetadata(footer, fs, rowGroup.getPath().toString(),
readerConfig);
+
+              // The file status for this file
+              FileStatus fileStatus = fs.getFileStatus(rowGroup.getPath());
+              List<FileStatus> listFileStatus = new ArrayList<>(Arrays.asList(fileStatus));
+              List<Path> listRowGroupPath = new ArrayList<>(Arrays.asList(rowGroup.getPath()));
+              List<ReadEntryWithPath> entries = new ArrayList<>(Arrays.asList(new
ReadEntryWithPath(rowGroup.getPath())));
+              fileSelection = new FileSelection(listFileStatus, listRowGroupPath, selectionRoot);
+
+              metadataProvider = new ParquetTableMetadataProviderImpl(entries, selectionRoot,
fileSelection.cacheFileRoot, readerConfig, fs,false);
+              // The file metadata (for all columns)
+              fileMetadataV3 = Metadata.getParquetFileMetadata_v3(tableMetadataV3, footer,
fileStatus, fs, true, null, readerConfig);
+
+              prevRowGroupPath = rowGroup.getPath(); // for next time
+            }
+
+            MetadataBase.RowGroupMetadata rowGroupMetadata = fileMetadataV3.getRowGroups().get(rowGroup.getRowGroupIndex());
+
+            Map<SchemaPath, ColumnStatistics> columnsStatistics = ParquetTableMetadataUtils.getRowGroupColumnStatistics(tableMetadataV3,
rowGroupMetadata);
+
+            List<SchemaPath> columns = columnsStatistics.keySet().stream().collect(Collectors.toList());
+
+            ParquetGroupScan parquetGroupScan = new ParquetGroupScan( context.getQueryUserName(),
metadataProvider, fileSelection, columns, readerConfig, filterExpr);
 
 Review comment:
   I am actually less concerned about the elapsed time and more about the number of objects
created on the Java heap.  The `ParquetGroupScan` is at least 100 bytes each and since we
are targeting use cases with about million row groups per minor fragment, it means 100 MB
per minor fragment (assuming the garbage collector is not doing the cleanup while the Foo
loop is executing).  If there are 24 minor frags, this would add up to 2.4GB heap per node
which would cause quite a bit of GC activity subsequently.  
   
   I have made some changes on top of your branch which avoids this by directly calling a
static method to create a FilterPredicate.   The pruning unit tests are passing with these
changes.  I will send my changes to you offline and we can discuss.     

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