Hi I am trying to write to Sybase IQ using JDBC from a file which contains thousands of rows. People say that I should use batchUpdate. So I am reading file by NIO and adding it to PreparedStatement batches. But I dont see any advantage here for all the rows I need to do the following
PreparedStatement prepStmt = con.prepareStatement(
"UPDATE DEPT SET MGRNO=? WHERE DEPTNO=?");
prepStmt.setString(1,mgrnum1);
prepStmt.setString(2,deptnum1);
prepStmt.addBatch();
I dont understand what is the advantage of batches. I have to anyhow execute addBatch for thousands of time for all the records of file. Or Should I even be using addBatch() to write records from a file to sybase iq. Please guide. Thanks a lot.
With batch updates, basically, you're cutting down on your Network I/O overhead. It's providing the benefits analogous to what a BufferedWriter provides you while writing to the disk. That's basically what this is: buffering of database updates.
Any kind of I/O has a cost; be it disk I/O or network. By buffering your inserts or updates in a batch and doing a bulk update you're minimizing the performance hit incurred every time you hit the database and come back.
The performance hit becomes even more obvious in case of a real world application where the database server is almost always under some load serving other clients as opposed to development where you're the only one.
When paired with a PreparedStatement the bulk updates are even more efficient because the Statement is pre-compiled and the execution plan is cached as well throughout the execution of the batch. So, the binding of variables happen as per your chosen batch size and then a single batchUpdate() call persists all the values in one go.
The advantage of addBatch is that it allows the jdbc driver to write chunks of data instead of sending single insert statements to the database.
This can be faster in certain situations, but real life performance may vary.
It should also be noticed that it's recommended to use batches of 50-100 rows, instead of adding all the data into a single batch.
Related
I have a JAVA application that can use a SQL database from any vendor. Right now we have tested Vertica and PostgreSQL. I want to export all the data from one table in the DB and import it later on in a different instance of the application. The size of the DB is pretty big so there are many rows in there. The export and import process has to be done from inside the java code.
What we've tried so far is:
Export: we read the whole table (select * from) through JDBC and then dump it to an SQL file with all the INSERTS needed.
Import: The file containing those thousands of INSERTS is executed in the target database through JDBC.
This is not an efficient process. Firstly, the select * from part is giving us problems because of the size of it and secondly, executing a lot if inserts one after another gives us problems in Vertica (https://forum.vertica.com/discussion/235201/vjdbc-5065-error-too-many-ros-containers-exist-for-the-following-projections)
What would be a more efficient way of doing this? Are there any tools that can help with the process or there is no "elegant" solution?
Why not do the export/import in a single step with batching (for performance) and chunking (to avoid errors and provide a checkpoint where to start off after a failure).
In most cases, databases support INSERT queries with many values, e.g.:
INSERT INTO table_a (col_a, col_b, ...) VALUES
(val_a, val_b, ...),
(val_a, val_b, ...),
(val_a, val_b, ...),
...
The number of rows you generate into a single such INSERT statement is then your chunk-size, which might need tuning for the specific target database (big enough to speed things up but small enough to make the chunk not exceed some database limit and create failures).
As already proposed, each of this chunk should then be executed in a transaction and your application should remember which chunk it successfully executed last in case some error occurs so it can continue at the next run there.
For the chunks itself, you really should use LIMIT OFFSET .
This way, you can repeat any chunk at any time, each chunk by itself is atomic and it should perform much better than with single row statements.
I can only speak about PostgreSQL.
The size of the SELECT is not a problem if you use server-side cursors by calling setFetchSize with a value greater than 0 (perhaps 10000) on the statement.
The INSERTS will perform well if
you run them all in a single transaction
you use a PreparedStatement for the INSERT
Each insert into Vertica goes into WOS (memory), and periodically data from WOS gets moved to ROS (disk) into a single container. You can only have 1024 ROS containers per projection per node. Doing many thousands of INSERTs at a time is never a good idea for Vertica. The best way to do this is to copy all that data into a file and bulk load the file into Vertica using the COPY command.
This will create a single ROS container for the contents of the file. Depending on how many rows you want to copy it will be many times (sometimes even hundreds of times) faster.
https://www.vertica.com/docs/9.2.x/HTML/Content/Authoring/SQLReferenceManual/Statements/COPY/COPY.htm
https://www.vertica.com/docs/9.2.x/HTML/Content/Authoring/ConnectingToVertica/ClientJDBC/UsingCOPYLOCALWithJDBC.htm
I have to read huge data from the database (for example lets consider more than 500 000 records). Then I have to save the read data to a file. I have many issues with cursor (not only memory issue).
Is it possible to do it without cursor, for example using stream? If so how can I achieve it?
I have experienced working with huge data (almost 500 milions of records). I simply used PreparedStatement query, ResultSet and of cource some buffer tweaking through:
setFetchSize(int)
In my case, i split the program into threads because the huge table was partitioned (each thread processed one partition) but i think that this is not your case.
It is pointless to fetch data through cursor. I would rather use the database view or SQL query. Do not use ORM for this purpose.
According to your comment, your best option is to limit JDBC to fetch only specific number of rows instead of fetching all of them (this helps to begin processing faster and does not load entire table into ResultSet). Save your data into collection and write it into file using BufferedWriter. You can also benefit from multi-core CPU to make it run in more threads - like first fetched rows run in 1 thread, other fetched rows in second thread. In case of threading, use synchronized collections and be aware that you might face the problem of ordering.
I'm sending a long list of updates to a database from a Java-program. I'm wondering if there's a speed difference between
Putting all the updates in one query and execute that
Making a preparedStatement, adding every update to the batch and executing the batch
Using PreparedStatement and batching would be the preferred approach. It reduces the network traffic between the client and the database server.
Yes it does!
It will reduce the traffic between application and server.
I know you mentioned java but just as an example, this is a hint from a C# book Im reading :
NOTE FREE PERFORMANCE UPGRADE!
Setting UpdateBatchSize to 0 is a quick way to boost the update performance of the
DbDataAdapter object. (Setting the value to 0 instructs the DbDataAdapter object to create the largest possible batch size for changes)
I have one application where "persisting to database" is consuming 85% time of the entire application flow.
I was thinking of using multiple threads to do the insert because inserts are mostly independent here. Is there any way to achieve multi threaded insert using any of JPA implementation ? Or is it worth doing the mutli threaded insert, from improving the performance perspective ?
Note: Inserts are in the range of 10K to 100K records in a single run. Also performance is very very critical here.
Thanks.
Multi-threading insert statements on database won't really make it perform any faster because in most databases the table requires a lock for an insert. So your threads will just be waiting for the one before it to finish up and unlock the table before the next can insert - which really doesn't make it any more multi-threaded than with a single thread. If you where to do it, it would most likely slow it down.
If you inserting 10k-100k records you should consider using either batch insert statements or bulk insert commands that are native to the database your using. The fastest way would be the native bulk insert commands but it would require you to not use JPA and to work directly with JDBC calls for the inserts you want to use bulk commands on.
If you don't want to play around with native bulk commands I recommend using Spring's JDBCTemplate which has templated batch insert commands. It is very fast and I use it to batch insert 10k-20k entities every 30 seconds on a high transaction system and I am very pleased with the performance.
Lastly, make sure your database tables are optimized with the correct indexes, keys and options. Since your database is the bottleneck this should be one of the first places you look to increase performance.
Multi-threading insert statements on database won't really make it perform any faster
because in most databases the table requires a lock for an insert. So your threads will
just be waiting for the one before it to finish up and unlock the table before the next can
insert - which really doesn't make it any more multi-threaded than with a single thread. If
you where to do it, it would most likely slow it down.
Are you saying concurrent inserts from different db connections on the same table require exclusive locks to complete? I tested this on Oracle, and I didn't find this to be the case. Do you actually have a test case to back up what you wrote here?
Anyway, bulk insert is of course a lot faster than one insert at a time.
Are you periodically flushing your session when doing this? if not, you can hit nasty slowdowns that have nothing to do with the database. generally, you want to "batch" the inserts by periodically calling flush() then clear() on your session (assuming you are using some variant of JPA).
This article has many tips to improve batch writing performance with JPA. I'll quote the two that should give you the best result for fast reference.
Optimization #6 - Sequence
Pre-allocation
We have optimized the
first part of the application, reading
from the MySQL database. The second
part is to optimize the writing to
Oracle.
The biggest issue with the writing
process is that the Id generation is
using an allocation size of 1. This
means that for every insert there will
be an update and a select for the next
sequence number. This is a major
issue, as it is effectively doubling
the amount of database access. By
default JPA uses a pre-allocation size
of 50 for TABLE and SEQUENCE Id
generation, and 1 for IDENTITY Id
generation (a very good reason to
never use IDENTITY Id generation). But
frequently applications are
unnecessarily paranoid of holes in
their Id values and set the
pre-allocaiton value to 1. By changing
the pre-allocation size from 1 to 500,
we reduce about 1000 database accesses
per page.
Optimization #8 - Batch Writing
Many
databases provide an optimization that
allows a batch of write operations to
be performed as a single database
access. There is both parametrized and
dynamic batch writing. For
parametrized batch writing a single
parametrized SQL statement can be
executed with a batch of parameter
vales instead of a single set of
parameter values. This is very optimal
as the SQL only needs to be executed
once, and all of the data can be
passed optimally to the database.
Dynamic batch writing requires dynamic
(non-parametrized) SQL that is batched
into a single big statement and sent
to the database all at once. The
database then needs to process this
huge string and execute each
statement. This requires the database
do a lot of work parsing the
statement, so is no always optimal. It
does reduce the database access, so if
the database is remote or poorly
connected with the application, this
can result in an improvement.
In general parametrized batch writing
is much more optimal, and on Oracle it
provides a huge benefit, where as
dynamic does not. JDBC defines the API
for batch writing, but not all JDBC
drivers support it, some support the
API but then execute the statements
one by one, so it is important to test
that your database supports the
optimization before using it. In
EclipseLink batch writing is enabled
using the persistence unit property
"eclipselink.jdbc.batch-writing"="JDBC".
Another important aspect of using
batch writing is that you must have
the same SQL (DML actually) statement
being executed in a grouped fashion in
a single transaction. Some JPA
providers do not order their DML, so
you can end up ping-ponging between
two statements such as the order
insert and the order-line insert,
making batch writing in-effective.
Fortunately EclipseLink orders and
groups its DML, so usage of batch
writing reduces the database access
from 500 order inserts and 5000
order-line inserts to 55 (default
batch size is 100). We could increase
the batch size using
"eclipselink.jdbc.batch-writing.size",
so increasing the batch size to 1000
reduces the database accesses to 6 per
page.
i'm parsing large log files (5+GB) and extracting ad-hoc placed profiling lines (call name and execution time). I want to insert those lines into a MySql db.
My question is: should I execute the insert statement every time I get the line while parsing or there's some best practice to speed up everything?
If there is any way that you could do a bulk insert, that would help a lot (or at least send your data to the database in batches, instead of making separate calls each time).
Edit
LOAD DATA INFILE sounds even faster ;o)
https://web.archive.org/web/20150413042140/http://jeffrick.com/2010/03/23/bulk-insert-into-a-mysql-database
There are better options.
See http://dev.mysql.com/doc/refman/5.0/en/insert-speed.html
In your case, I think writing the relevant records to a file and then using LOAD DATA INFILE is the best approach.
For small updates, the number of transactions is critical for performance. SO if you can perform a number of inserts in the same transaction it will go much faster. I would try 100 inserts per transaction first.
If you don't want to follow the recommendations in Galz's link ( which is excellent BTW ) then try to open the connection and prepare the statement once, then loop round your log files carrying out the inserts ( using the premared statement ), then finally close the statement and connection once at the end. It's not the fastest way of doing the inserts, but it's the fastest way that sticks to a "normal" JDBC approach.
From java
JDBC batch insert
Example:
You do this with every insert: http://code.google.com/p/hunglish-webapp/source/browse/trunk/src/main/java/hu/mokk/hunglish/lucene/Indexer.java#232
You do this with every batch http://code.google.com/p/hunglish-webapp/source/browse/trunk/src/main/java/hu/mokk/hunglish/lucene/Indexer.java#371
The size of the batch can be determined by the available memory.
Aside from insert speed, the other problem you may run into is memory. Whatever approach you use, you will still need to consider your memory usage as the records are loaded from the file. Unless you have a hard requirement on processing speed, then it may be a better to use an approach with a predictable memory foot print.