SERVER-29817 Always intialize bytesWritten to 0 for chunks.

Previously, it was initialized to a pseudorandom value that was less than
some fraction of the maximum chunk size. This introduced a depencency between
the chunk constuctor and the balancer, and provided no particular value.

3 files changed, 3 insertions, 26 deletions

diff --git a/src/mongo/s/chunk.cpp b/src/mongo/s/chunk.cpp
index 72651dec9f6..3c183a15885 100644
--- a/src/mongo/s/chunk.cpp
+++ b/src/mongo/s/chunk.cpp
@@ -32,34 +32,16 @@
 
 #include "mongo/s/chunk.h"
 
-#include "mongo/platform/random.h"
-#include "mongo/s/balancer_configuration.h"
-#include "mongo/s/grid.h"
-#include "mongo/util/log.h"
+#include "mongo/util/mongoutils/str.h"
 
 namespace mongo {
-namespace {
-
-// Test whether we should split once data * splitTestFactor > chunkSize (approximately)
-const int splitTestFactor = 5;
-
-/**
- * Generates a random value for _dataWritten so that a mongos restart wouldn't cause delay in
- * splitting.
- */
-int64_t mkDataWritten() {
-    PseudoRandom r(static_cast<int64_t>(time(0)));
-    return r.nextInt32(grid.getBalancerConfiguration()->getMaxChunkSizeBytes() / splitTestFactor);
-}
-
-}  // namespace
 
 Chunk::Chunk(const ChunkType& from)
     : _range(from.getMin(), from.getMax()),
       _shardId(from.getShard()),
       _lastmod(from.getVersion()),
       _jumbo(from.getJumbo()),
-      _dataWritten(mkDataWritten()) {
+      _dataWritten(0) {
     invariantOK(from.validate());
 }
 
@@ -80,10 +62,6 @@ void Chunk::clearBytesWritten() {
     _dataWritten = 0;
 }
 
-void Chunk::randomizeBytesWritten() {
-    _dataWritten = mkDataWritten();
-}
-
 std::string Chunk::toString() const {
     return str::stream() << ChunkType::shard() << ": " << _shardId << ", " << ChunkType::lastmod()
                          << ": " << _lastmod.toString() << ", " << _range.toString();
diff --git a/src/mongo/s/chunk.h b/src/mongo/s/chunk.h
index 484a1d9597c..af89044f41c 100644
--- a/src/mongo/s/chunk.h
+++ b/src/mongo/s/chunk.h
@@ -80,7 +80,6 @@ public:
     uint64_t getBytesWritten() const;
     uint64_t addBytesWritten(uint64_t bytesWrittenIncrement);
     void clearBytesWritten();
-    void randomizeBytesWritten();
 
     /**
      * Marks this chunk as jumbo. Only moves from false to true once and is used by the balancer.
diff --git a/src/mongo/s/commands/cluster_write.cpp b/src/mongo/s/commands/cluster_write.cpp
index 0bc72d6fd7c..ecc68ae8b0c 100644
--- a/src/mongo/s/commands/cluster_write.cpp
+++ b/src/mongo/s/commands/cluster_write.cpp
@@ -452,7 +452,7 @@ void updateChunkWriteStatsAndSplitIfNeeded(OperationContext* opCtx,
         // Ensure the collection gets reloaded because of the move
         Grid::get(opCtx)->catalogCache()->invalidateShardedCollection(nss);
     } catch (const DBException& ex) {
-        chunk->randomizeBytesWritten();
+        chunk->clearBytesWritten();
 
         if (ErrorCodes::isStaleShardingError(ErrorCodes::Error(ex.getCode()))) {
             log() << "Unable to auto-split chunk " << redact(chunkRange.toString()) << causedBy(ex)