I created a database with a table named flagTable, this table only has two fields, which are id(auto increment) and an integer field. Next, in my program, I have a button that will trigger a thread to start. When the thread is starting, it constantly retrieve data from database, and check for the for the value, if the value is equal to one then it will trigger another new Thread, something like this:
private class statusOfStrummingInAnotherDevice extends Thread {
int value;
public void run() {
try{
while(true){
try{
if(flagCursor == null){
flagCursor = cdb1.getFlagAll();
}
}catch(Exception e){break;}
try{
Log.i("MAIN3ACTIVITY","getting status");
int size = cdb1.getSize(flagCursor);
Log.i("MAIN3ACTIVITY","SIZE is" + String.valueOf(xyz));
for(int i = 0 ; i < size ; i++){
flagCursor.moveToPosition(i);
Log.i("MAIN3ACTIVITY","getting status jkasdfasdf");
value = cdb1.getFlag();
if(value == 1){
Log.i("FLAGCURSOR=====>>>>","Succesful");
releasingNotes = new ReleasingNotes(IntendedChord);
releasingNotes.start();
//break;
}
cdb1.updateFlag(0);
Log.i("FLAGCURSOR=====>>>>",String.valueOf(value));
}
flagCursor = null;
}catch(Exception e){break;}
Log.i("MAIN3ACTIVITY","thread is sleeping");
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
break;
}
}
}catch(Exception e){
}
}
}
In the meantime, the data that were retrieved from the database is using this function:
public Cursor getFlagAll(){
return getReadableDatabase().rawQuery(
"SELECT _ID, flag from flagTable", null);
}
And, the data that were updated to the database through this method:
public int updateFlag(int i) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues contentValues = new ContentValues();
contentValues.put("flag",i);
return db.update("flagTable" , contentValues , "_ID" + "= ?",new String[]{String.valueOf(1)});
}
Now, above codes will give no error, however, the data that were retrieved from the database is always 1, it keeps trigger a new function. In my above codes, I stated if the value is equal to 1, then the current thread will trigger a new thread to start, When its finished, the program will update the current data to 0. So that, the next round of the infinite loop can stop triggering new thread until a the conditon is met. What is problem overhere? did my codes really updated the new value? or I need to referesh the database every time I updated a new value.
Use Listeners to your database.
use SQLiteTransactionListener and do your things in onCommit()
Some guide in details here :
https://developer.android.com/reference/android/database/sqlite/SQLiteTransactionListener.html and
http://www.programcreek.com/java-api-examples/index.php?api=android.database.sqlite.SQLiteTransactionListener
I'm using a cursor in a while loop to execute multiple queries on my database, so each time Content Resolver returns new cursor object instance. I am uncertain about proper way I should reuse the cursor during each iteration of the loop:
Close it once, after all operations being performed
Cursor c;
try {
while(condition) {
c = Context.getContentResolver().query(...);
// fetching values
}
} finally {
if (c != null) {
c.close()
}
}
Close it at the end of each iteration
Cursor c;
try {
while(condition) {
c = Context.getContentResolver().query(...);
// fetching values
if (c != null) {
c.close()
}
}
} finally {
if (c != null) {
c.close()
}
}
Create new cursor variable inside while loop
while(condition) {
Cursor c = Context.getContentResolver().query(...);
try {
// fetching values
} finally {
if (c != null) {
c.close()
}
}
}
?
Case 1 is bad since you're assigning a new cursor in your loop and you only get to close the last assigned cursor.
Case 2 and 3 are very similar but I prefer case 3 because with case 2 you can break out of your loop unexpectedly but with case 3 you keep the cursor in the loop scope and the loop can keep running.
In your examples the third variant is most useful because you open-close the same Cursor object in each loop. You lost nothing: niether memory leaks no app+db crashes.
I have a method which reads data from file line by line and takes value between coma, then puts this value into INSERT query. Data in file saved in this way:
–,08:10,–,20:20,08:15,08:16,20:26,20:27,08:20,08:21,20:31,20:32,08:30,08:31,20:40,20:41,08:37,08:38,20:46
20:47,08:48,08:50,20:56,20:57,09:00,09:01,21:07,21:08
08:53,–,17:43,09:01,09:03,09:13,09:15,18:02,18:04,–,–,09:19,09:25
Here is actual my code:
public void insertTime(SQLiteDatabase database, String table) throws FileNotFoundException {
BufferedReader br = null;
String line;
try {
int j = 0;
br = new BufferedReader(new InputStreamReader(context.getAssets().open("time.txt")));
database.beginTransaction();
while ((line = br.readLine()) != null) {
j++;
String query = "INSERT INTO "+table+""+j+" (arrival, departure) VALUES (?,?)";
SQLiteStatement statement = database.compileStatement(query);
// use comma as separator
String[] time = line.split(",");
for(int i = 1; i < time.length; i+=2) {
statement.bindString(1,time[i-1]);//arrival
statement.bindString(2,time[i]);//departure
statement.executeInsert();
statement.clearBindings();
}
}
database.setTransactionSuccessful();
database.endTransaction();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (br != null) {
try {
br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
The problem is that data insert very slow, despite I use SQLiteStatement and transactions. For example, when I insert 69000 rows it takes about 65,929 seconds.
What have I to change in my code to improve speed of insertion ?
UPDATE
OK, I have simplified my code, I got rid of BufferedReader and now it looks like this
public void insertTime(SQLiteDatabase database) throws FileNotFoundException {
database.beginTransaction();
int r = 0;
while (r < 122) {
r++;
String query = "INSERT INTO table_1 (arrival, departure) VALUES (?,?)";
SQLiteStatement statement = database.compileStatement(query);
for(int i = 1; i < 1100; i++) {
statement.bindString(1,i+"");//arrival
statement.bindString(2,i+"");//departure
statement.executeInsert();
statement.clearBindings();
}
}
database.setTransactionSuccessful();
database.endTransaction();
}
But it still so long inserts data, more than 2 min. Do you have any ideas how to increase speed of my second example ?
Here is a very very detailed post on every method of increasing SQL insertion speed.
Move beginTransaction() and setTransactionSuccessful() outside of while loop and it will be way faster.
A new transaction is started for each item in the while() loop.
It might go a bit faster if you only have 1 transaction to do all your insertions.
Also, when your data is corrupt and String.split doesn't give you at least 2 items, then your transaction will not be ended properly due to an Exception being thrown.
Every time you insert a row in a table with indexes, the indexes have to be adjusted. That operation can be costly. Indexes are kept as b-trees and if you hit the rebalance point, you're bound to have a slowdown. One thing you can do to test this is to remove your indexes. You could also drop the indexes, insert, then re-create the indexes.
For those using JDBC (Java): to be sure, do you first set the autoCommit to FALSE?
I guess so, because you work with explicit transactions.
The performace gain I got by explicitly setting the autocommit off was over 1000 times!
So:
Class.forName("org.sqlite.JDBC");
String urlInput = "jdbc:sqlite:" + databaseFile;
databaseConnection = DriverManager.getConnection(urlInput);
databaseConnection.setAutoCommit( false);
And:
String sql = "INSERT INTO " + TABLE_NAME + " ( type, bi, ci, fvi, tvi, content_type) VALUES ('V',?,?,?,?,'rtf')";
PreparedStatement psi = databaseConnection.prepareStatement(sql);
for( Item item : items) {
psi.setInt(1, item.property1);
// ....
count = psi.executeUpdate();
}
databaseConnection.commit();
databaseConnection.setAutoCommit( true);
So, when somebody forgets this, this may have a huge effect.
I have created a table and trying to fetch data from it using a cursor as follow:
public Cursor getcontent() {
Cursor d = database.query(DatabaseHandler.Table_Name2,allColumns,selection, null, null,null,null);
return d;
}
Cursor r = X.getcontent();
if (r.getCount() > 0) {
r.moveToFirst();
do {
String id = r.getString(r.getColumnIndex("content_id"));
al.add(id);
MainActivity.tt1.append("\n");
MainActivity.tt1.append(id);
} while (r.moveToNext()==true);
r.close();
} else {
Log.i("TAG"," No value found");
}
}
I am showing the result in the TextView to see what data it is fetched. My problem is when I run this code sometimes it shows the data in the TextView, whatever it has fetched and sometimes it doesn't. Its a 50:50 ratio, according to me it should show fetched values every time as data is fetched every time I don't know what is wrong here, can someone tell me what's the issue here?
Check Whether Cursor you are getting is Null or not . and if yes then What is the Count of Cursor. you can Do it by Below Way.
Cursor r = X.getcontent();
if ((r != null) && (r.getCount() > 0)) {
r.moveToFirst();
do {
String id = r.getString(r.getColumnIndex("content_id"));
al.add(id);
MainActivity.tt1.append("\n");
MainActivity.tt1.append(id);
} while (r.moveToNext());
r.close();
} else {
Log.i("TAG"," No value found inside Cursor");
}
try like this
Cursor r = X.getcontent();
try {
if (r.moveToFirst()) {
do {
String id = r.getString(r.getColumnIndex("content_id"));
al.add(id);
MainActivity.tt1.append("\n");
MainActivity.tt1.append(id);
} while (r.moveToNext());
}
} finally {
if(r!=null) {
r.close();
}
}
I have written a simple code for Database updatation, but it is sometime updating and sometimes not... i have written LOG for conformation but the log is giving correct output. Here is what i am trying :=
public void updateDownloadedAssetNumberOfStartingBytesEncrypted(int id, int startingBytesEncrypted)
{
SQLiteDatabase database = null;
int numOfRowsUpdated = 0;
try
{
database = getWritableDatabase();
ContentValues values = new ContentValues();
values.put("StartingBytesEncrypted", startingBytesEncrypted);
if(database.isOpen())
{
Log.v("updating in db","doc id - "+id + " encrypted bytes - "+startingBytesEncrypted);
numOfRowsUpdated = database.update("_assets", values, "Id = "+id, null);
}
else
{
Log.v("Database","the database is not open thus starting encrypted bytes were not updated");
}
Log.v("muber of rows updated - ",""+numOfRowsUpdated);
}
catch(Exception ex)
{
}
finally
{
if(database != null)
{
database.close();
}
}
}
What is the problem?? Any help would be Appreciable.
Ya i got ur code...
Finally i resolved the issue.... actually it is beacuse of threading....
the thread creating the row was executed later and that updating the row was executed first
i have resolved it.Have fun :)
This happened due to connection of database is not open. Pls keep ex.printstacktrace(); in catch statement.