Return count of rows in a resultset only once (when startPos = 0)

If a query returns 100 rows and say only 10 rows fit in 1MB, then client
receiving the cursor from the ContentProvider needs to paginate.
ContentProvider returns count of total data everytime it returns a page
(= 1MB) of data to the client.
Returning total count causes reading (and skipping unwanted) data
from sqlite.
Instead, it should be sufficient to get total count once
and re-use the count value during the life of the cursor
until a requery is performed on the cursor.
(Count won't change unless data is changed - in which case
the cursor is asked to perform requery anyway. So doing count
once and reusing it should work)
Change-Id: I3520d94524dda07be9bcff56b6fbae5276af1d3b

1 files changed, 32 insertions, 14 deletions

diff --git a/core/jni/android_database_SQLiteQuery.cpp b/core/jni/android_database_SQLiteQuery.cpp
index e383123..d18cfd8 100644
--- a/core/jni/android_database_SQLiteQuery.cpp
+++ b/core/jni/android_database_SQLiteQuery.cpp
@@ -15,7 +15,7 @@
  */
 
 #undef LOG_TAG
-#define LOG_TAG "Cursor"
+#define LOG_TAG "SqliteCursor.cpp"
 
 #include <jni.h>
 #include <JNIHelp.h>
@@ -116,6 +116,7 @@ static jint native_fill_window(JNIEnv* env, jobject object, jobject javaWindow,
     int retryCount;
     int boundParams;
     CursorWindow * window;
+    bool gotAllRows = true;
     
     if (statement == NULL) {
         LOGE("Invalid statement in fillWindow()");
@@ -131,8 +132,7 @@ static jint native_fill_window(JNIEnv* env, jobject object, jobject javaWindow,
         err = sqlite3_bind_int(statement, offsetParam, startPos);
         if (err != SQLITE_OK) {
             LOGE("Unable to bind offset position, offsetParam = %d", offsetParam);
-            jniThrowException(env, "java/lang/IllegalArgumentException",
-                              sqlite3_errmsg(GET_HANDLE(env, object)));
+            throw_sqlite3_exception(env, GET_HANDLE(env, object));
             return 0;
         }
         LOG_WINDOW("Bound to startPos %d", startPos);
@@ -182,7 +182,8 @@ static jint native_fill_window(JNIEnv* env, jobject object, jobject javaWindow,
                 field_slot_t * fieldDir = window->allocRow();
                 if (!fieldDir) {
                     LOGE("Failed allocating fieldDir at startPos %d row %d", startPos, numRows);
-                    return startPos + numRows + finish_program_and_get_row_count(statement) + 1;
+                    gotAllRows = false;
+                    goto return_count;
                 }
             }
 
@@ -207,7 +208,8 @@ static jint native_fill_window(JNIEnv* env, jobject object, jobject javaWindow,
                         window->freeLastRow();
                         LOGD("Failed allocating %u bytes for text/blob at %d,%d", size,
                                    startPos + numRows, i);
-                        return startPos + numRows + finish_program_and_get_row_count(statement) + 1;
+                        gotAllRows = false;
+                        goto return_count;
                     }
 
                     window->copyIn(offset, text, size);
@@ -225,8 +227,9 @@ static jint native_fill_window(JNIEnv* env, jobject object, jobject javaWindow,
                     int64_t value = sqlite3_column_int64(statement, i);
                     if (!window->putLong(numRows, i, value)) {
                         window->freeLastRow();
-                        LOGD("Failed allocating space for a long in column %d", i);
-                        return startPos + numRows + finish_program_and_get_row_count(statement) + 1;
+                        LOGE("Failed allocating space for a long in column %d", i);
+                        gotAllRows = false;
+                        goto return_count;
                     }
                     LOG_WINDOW("%d,%d is INTEGER 0x%016llx", startPos + numRows, i, value);
                 } else if (type == SQLITE_FLOAT) {
@@ -234,8 +237,9 @@ static jint native_fill_window(JNIEnv* env, jobject object, jobject javaWindow,
                     double value = sqlite3_column_double(statement, i);
                     if (!window->putDouble(numRows, i, value)) {
                         window->freeLastRow();
-                        LOGD("Failed allocating space for a double in column %d", i);
-                        return startPos + numRows + finish_program_and_get_row_count(statement) + 1;
+                        LOGE("Failed allocating space for a double in column %d", i);
+                        gotAllRows = false;
+                        goto return_count;
                     }
                     LOG_WINDOW("%d,%d is FLOAT %lf", startPos + numRows, i, value);
                 } else if (type == SQLITE_BLOB) {
@@ -247,7 +251,8 @@ static jint native_fill_window(JNIEnv* env, jobject object, jobject javaWindow,
                         window->freeLastRow();
                         LOGD("Failed allocating %u bytes for blob at %d,%d", size,
                                    startPos + numRows, i);
-                        return startPos + numRows + finish_program_and_get_row_count(statement) + 1;
+                        gotAllRows = false;
+                        goto return_count;
                     }
 
                     window->copyIn(offset, blob, size);
@@ -306,12 +311,24 @@ static jint native_fill_window(JNIEnv* env, jobject object, jobject javaWindow,
 
     LOG_WINDOW("Resetting statement %p after fetching %d rows in %d bytes\n\n\n\n", statement,
             numRows, window->size() - window->freeSpace());
-//    LOGI("Filled window with %d rows in %d bytes", numRows, window->size() - window->freeSpace());
+    LOG_WINDOW("Filled window with %d rows in %d bytes", numRows,
+            window->size() - window->freeSpace());
     if (err == SQLITE_ROW) {
+        // there is more data to be returned. let the caller know by returning -1
         return -1;
-    } else {
+    }
+  return_count:
+    if (startPos) {
         sqlite3_reset(statement);
-        return startPos + numRows;
+        LOG_WINDOW("Not doing count(*) because startPos %d is non-zero", startPos);
+        return 0;
+    } else if (gotAllRows) {
+        sqlite3_reset(statement);
+        LOG_WINDOW("Not doing count(*) because we already know the count(*)");
+        return numRows;
+    } else {
+        // since startPos == 0, we need to get the count(*) of the result set
+        return numRows + 1 + finish_program_and_get_row_count(statement);
     }
 }
 
@@ -336,7 +353,8 @@ static jstring native_column_name(JNIEnv* env, jobject object, jint columnIndex)
 static JNINativeMethod sMethods[] =
 {
      /* name, signature, funcPtr */
-    {"native_fill_window", "(Landroid/database/CursorWindow;IIII)I", (void *)native_fill_window},
+    {"native_fill_window", "(Landroid/database/CursorWindow;IIII)I",
+            (void *)native_fill_window},
     {"native_column_count", "()I", (void*)native_column_count},
     {"native_column_name", "(I)Ljava/lang/String;", (void *)native_column_name},
 };