[GitHub] [incubator-iceberg] rdblue commented on a change in pull request #675: Inherit snapshot ids for manifest entries

[GitBox <gi...@apache.org>]

rdblue commented on a change in pull request #675: Inherit snapshot ids for manifest entries
URL: https://github.com/apache/incubator-iceberg/pull/675#discussion_r364357342
 
 

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 File path: core/src/main/java/org/apache/iceberg/FastAppend.java
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 @@ -81,15 +83,21 @@ public FastAppend appendFile(DataFile file) {
 
   @Override
   public FastAppend appendManifest(ManifestFile manifest) {
-    // the manifest must be rewritten with this update's snapshot ID
-    try (ManifestReader reader = ManifestReader.read(
-        ops.io().newInputFile(manifest.path()), ops.current().specsById())) {
-      OutputFile newManifestPath = manifestPath(manifestCount.getAndIncrement());
-      appendManifests.add(ManifestWriter.copyAppendManifest(reader, newManifestPath, snapshotId(), summaryBuilder));
+    Preconditions.checkArgument(!manifest.hasExistingFiles(), "Cannot append manifest with existing files");
+    Preconditions.checkArgument(!manifest.hasDeletedFiles(), "Cannot append manifest with deleted files");
+    Preconditions.checkArgument(manifest.snapshotId() == null, "Snapshot id must be assigned during commit");
+
+    // TODO: avoid reading manifests to simply get stats
+    try (ManifestReader reader = ManifestReader.read(manifest, ops.io(), ops.current().specsById())) {
 
 Review comment:
   Ideally, we would produce all of the summary stats, but the most important ones are `total-data-files`, `total-records`, and the `added-` or `deleted-` properties that are used to produce totals. I think it's okay to not write the `changed-partition-count` metrics if they require scanning the appended manifest.
   
   I think my response was confusing because we keep additional summary information about each partition in our version. I can move that upstream if everyone wants it, but it can make the metadata files quite large. Without a use case for doing this upstream, I didn't think it was a good idea to make everyone's metadata significantly larger.

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