SERVER-19183: Allow storage engines to provide optimized random cursors for use by $sample

1 files changed, 182 insertions, 0 deletions

diff --git a/src/mongo/db/storage/record_store_test_randomiter.cpp b/src/mongo/db/storage/record_store_test_randomiter.cpp
new file mode 100644
index 00000000000..a5921890a03
--- /dev/null
+++ b/src/mongo/db/storage/record_store_test_randomiter.cpp
@@ -0,0 +1,182 @@
+// record_store_test_randomiter.cpp
+
+/**
+ *    Copyright (C) 2014 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/db/storage/record_store_test_harness.h"
+
+
+#include "mongo/db/record_id.h"
+#include "mongo/db/storage/record_data.h"
+#include "mongo/db/storage/record_store.h"
+#include "mongo/unittest/unittest.h"
+
+using std::unique_ptr;
+using std::set;
+using std::string;
+using std::stringstream;
+
+namespace mongo {
+
+// Create a random iterator for empty record store.
+TEST(RecordStoreTestHarness, GetRandomIteratorEmpty) {
+    unique_ptr<HarnessHelper> harnessHelper(newHarnessHelper());
+    unique_ptr<RecordStore> rs(harnessHelper->newNonCappedRecordStore());
+
+    {
+        unique_ptr<OperationContext> opCtx(harnessHelper->newOperationContext());
+        ASSERT_EQUALS(0, rs->numRecords(opCtx.get()));
+    }
+
+    {
+        unique_ptr<OperationContext> opCtx(harnessHelper->newOperationContext());
+        auto cursor = rs->getRandomCursor(opCtx.get());
+        // returns NULL if getRandomCursor is not supported
+        if (!cursor) {
+            return;
+        }
+        ASSERT(!cursor->next());
+    }
+}
+
+// Insert multiple records and create a random iterator for the record store
+TEST(RecordStoreTestHarness, GetRandomIteratorNonEmpty) {
+    unique_ptr<HarnessHelper> harnessHelper(newHarnessHelper());
+    unique_ptr<RecordStore> rs(harnessHelper->newNonCappedRecordStore());
+
+    {
+        unique_ptr<OperationContext> opCtx(harnessHelper->newOperationContext());
+        ASSERT_EQUALS(0, rs->numRecords(opCtx.get()));
+    }
+
+    const unsigned nToInsert =
+        5000;  // should be non-trivial amount, so we get multiple btree levels
+    RecordId locs[nToInsert];
+    for (unsigned i = 0; i < nToInsert; i++) {
+        unique_ptr<OperationContext> opCtx(harnessHelper->newOperationContext());
+        {
+            stringstream ss;
+            ss << "record " << i;
+            string data = ss.str();
+
+            WriteUnitOfWork uow(opCtx.get());
+            StatusWith<RecordId> res =
+                rs->insertRecord(opCtx.get(), data.c_str(), data.size() + 1, false);
+            ASSERT_OK(res.getStatus());
+            locs[i] = res.getValue();
+            uow.commit();
+        }
+    }
+
+    {
+        unique_ptr<OperationContext> opCtx(harnessHelper->newOperationContext());
+        ASSERT_EQUALS(nToInsert, rs->numRecords(opCtx.get()));
+    }
+
+    set<RecordId> remain(locs, locs + nToInsert);
+    {
+        unique_ptr<OperationContext> opCtx(harnessHelper->newOperationContext());
+        auto cursor = rs->getRandomCursor(opCtx.get());
+        // returns NULL if getRandomCursor is not supported
+        if (!cursor) {
+            return;
+        }
+
+        // Iterate documents and mark those visited, but let at least one remain
+        for (unsigned i = 0; i < nToInsert - 1; i++) {
+            // Get a new cursor once in a while, shouldn't affect things
+            if (i % (nToInsert / 8) == 0) {
+                cursor = rs->getRandomCursor(opCtx.get());
+            }
+            remain.erase(cursor->next()->id);  // can happen more than once per doc
+        }
+        ASSERT(!remain.empty());
+        ASSERT(cursor->next());
+
+        // We should have at least visited a quarter of the items if we're any random at all
+        // This should be enabled once the fix for WT-2032 is integrated:
+        // ASSERT_LT(remain.size(), nToInsert * 3 / 4);
+    }
+}
+
+// Insert a single record. Create a random iterator pointing to that single record.
+// Then check we'll retrieve the record.
+TEST(RecordStoreTestHarness, GetRandomIteratorSingleton) {
+    unique_ptr<HarnessHelper> harnessHelper(newHarnessHelper());
+    unique_ptr<RecordStore> rs(harnessHelper->newNonCappedRecordStore());
+
+    {
+        unique_ptr<OperationContext> opCtx(harnessHelper->newOperationContext());
+        ASSERT_EQ(0, rs->numRecords(opCtx.get()));
+    }
+
+    // Insert one record.
+    RecordId idToRetrieve;
+    {
+        unique_ptr<OperationContext> opCtx(harnessHelper->newOperationContext());
+        WriteUnitOfWork uow(opCtx.get());
+        StatusWith<RecordId> res = rs->insertRecord(opCtx.get(), "some data", 10, false);
+        ASSERT_OK(res.getStatus());
+        idToRetrieve = res.getValue();
+        uow.commit();
+    }
+
+    // Double-check that the record store has one record in it now.
+    {
+        unique_ptr<OperationContext> opCtx(harnessHelper->newOperationContext());
+        ASSERT_EQ(1, rs->numRecords(opCtx.get()));
+    }
+
+    {
+        unique_ptr<OperationContext> opCtx(harnessHelper->newOperationContext());
+        auto cursor = rs->getRandomCursor(opCtx.get());
+        // returns NULL if getRandomCursor is not supported
+        if (!cursor) {
+            return;
+        }
+
+        // We should be pointing at the only record in the store.
+
+        // Check deattaching / reattaching
+        cursor->savePositioned();
+        cursor->detachFromOperationContext();
+        opCtx = harnessHelper->newOperationContext();
+        cursor->reattachToOperationContext(opCtx.get());
+        cursor->restore();
+
+        auto record = cursor->next();
+        ASSERT_EQUALS(record->id, idToRetrieve);
+
+        // Iterator should either be EOF now, or keep returning the single existing document
+        for (int i = 0; i < 10; i++) {
+            record = cursor->next();
+            ASSERT(!record || record->id == idToRetrieve);
+        }
+    }
+}
+}  // namespace mongo