My last year's post "Enable CORS support in REST services with Spring 3.1" seems causing some confusion. I decided to create an example to show how to enable CORS with Spring rest api. The CorsFilter is same as before:
Below are 2 endpoints from EmployeeController.java:
The update method adds the header Access-Control-Allow-Origin with "*", but delete method doesn't. Therefore, the update method is enabled with CORS, but delete isn't. If delete endpoint is called, the following error will be shown in Chrome:
"cannot load http://localhost:8080/rest/employee/1. Origin http://127.0.0.1:8080 is not allowed by Access-Control-Allow-Origin."
However, the delete method is still invoked on the server side since the pre-flight request (OPTIONS)
allows DELETE method to be called.
The entire project can be downloaded from github. Following README to test it.
My intention was to disable/enable CORS support in each individual method by setting "Access-Control-Allow-Origin", but it seems not working as expected: Although the browser returns correct info, the method call is still invoked on the server side even Access-Control-Allow-Origin is not set. If you are allowed to enable all endpoints with CORS support, the code can be simplified as below:
The only difference is that addHeader("Access-Control-Allow-Origin") is moved out the if check. And then the update method can be simplified as:
The code can be downloaded from github too.
Monday, June 3, 2013
Wednesday, May 15, 2013
Add an existing project to a newly created git repository
I recently created a project on my local machine using maven archetype. See my previous post on how to generate a new project from installed maven catalog. I then got github.com created a repository for this project, for example: git@github.com:zhentao/test1.git
How can I associate my existing project with the newly created git repo? There are 2 ways to do it:
First option:
1. clone the git repo:
git clone git@github.com:zhentao/test1.git
It will clone the repo to test1 folder.
2. copy your existing project to test1 folder
cp -r /path/to/project /path/to/test1
3. commit and push all files
git add .
git commit -m "first commit"
git push -u origin master
Second option (more git style)
1. go to your project folder
cd /path/to/project
2. run the following commands:
git init
git add .
git commit -m "first commit"
git remote add origin git@github.com:zhentao/test1.git
The above commands associate your project to git remote repo.
3. run the following commands to to merge the conflict:
git fetch
git merge origin/master
--run it if conflicts exist
git mergetool
git commit
git push -u origin master
How can I associate my existing project with the newly created git repo? There are 2 ways to do it:
First option:
1. clone the git repo:
git clone git@github.com:zhentao/test1.git
It will clone the repo to test1 folder.
2. copy your existing project to test1 folder
cp -r /path/to/project /path/to/test1
3. commit and push all files
git add .
git commit -m "first commit"
git push -u origin master
Second option (more git style)
1. go to your project folder
cd /path/to/project
2. run the following commands:
git init
git add .
git commit -m "first commit"
git remote add origin git@github.com:zhentao/test1.git
The above commands associate your project to git remote repo.
3. run the following commands to to merge the conflict:
git fetch
git merge origin/master
--run it if conflicts exist
git mergetool
git commit
git push -u origin master
Tuesday, April 9, 2013
Riak: configure memory_backend
Riak supports several backends:
1. bitcask
2. memory
3. leveldb
4. multi
My recent project required me to use memory backend. I have a test server with 24GB memory. I tried to use 4GB as the max_memory. It seems quite easy at beginning, and I just followed the doc from basho.com. I just replace riak_kv_bitcask_backend with riak_kv_memory_backend:
1. bitcask
2. memory
3. leveldb
4. multi
My recent project required me to use memory backend. I have a test server with 24GB memory. I tried to use 4GB as the max_memory. It seems quite easy at beginning, and I just followed the doc from basho.com. I just replace riak_kv_bitcask_backend with riak_kv_memory_backend:
{riak_kv, [
{storage_backend, riak_kv_memory_backend},
Then I want to see how much data I can load with default configuration. I loaded a little over 11 million records, then riak crashed. Then I set max_memory to 4GB to add the following right under {eleveldb ... configuration:
{memory_backend, [
...,
{max_memory, 4096}, %% 4GB in megabytes
...
]}
Note that the following is copied from riak's doc. Then interesting, riak crashed with same number of records (11M+). I then changed it to 8192, but riak still crashed with the same number of records. I spent a couple days, and couldn't figure out the reason. I went to #riak IRC and asked the following question, and those folks were very responsive and solved my problem right away:
<zhentao> hi folks, how to configure the max_memory for memory_backend?
<@alexmoore> Hi zhentao<zhentao> Hi<zhentao> I added the following to config file:<zhentao> {memory_backend, [ {max_memory, 8192} %% 8GB in megabytes ]},<zhentao> but it didn't work<@alexmoore> In regards to your earlier question, if you don't specify a max_memory, or a TTL, the memory backend will continue to grow until it runs out of memory.<@alexmoore> Let me look at your config here<zhentao> it seems like that<zhentao> the node crashed after I loaded some data<zhentao> then I specify the max_memory to 8gb, and it still crashed with same amount of data<@alexmoore> How much RAM does the machine have?<sully_> Cluster health seems like it's degrading again. We're starting to see the same errors as before.<zhentao> 24 GB<sully_> We are planning to add 3 more nodes.<@evanmcc> zhentao: that's 8GB per vnode<@rzezeski> sully_ ok, can you tar.gz the latest log files again, that might allow me to find the cause before it gets rotated out by the logger<@jcaprice> zhentao: did you restart the node after adding the memory constraint?<sully_> Getting you the latest logs.<zhentao> yes, I restarted it<@evanmcc> zhentao: how many nodes, and what is your ring size?<@alexmoore> zhentao, how many physical machines do you have in your cluster, and what is your ring size?<zhentao> it is a test server and just one machine<@jcaprice> ring size?<zhentao> i am new to riak, and where to find th ring size?<@evanmcc> if you didn't set it, it's 64<@alexmoore> In your vm.args file<@evanmcc> so you're limiting memory to 8GB * 64<zhentao> let me check<@evanmcc> alexmoore: it's in app.config under riak_core<@evanmcc> ring_creation_size<@alexmoore> Whoops, make that the app.config<zhentao> it is 64<zhentao> {ring_creation_size, 64},<@evanmcc> so you want to change max memory to 128<@evanmcc> if you want to limit it at 8GB<@jcaprice> zhentao: max_memory limits the amount of memory used per vnode, not for the node itself<zhentao> @jcaprice, so what number I should use for max_memory for my test server?<@evanmcc> 128, like I said above<zhentao> 128 mb?<@evanmcc> yes<@jcaprice> as evanmcc said, you'll want 8192 / 64<zhentao> thx, let me try it
So in summary, {max_memory, 4096} is for each vnode, not for each machine. Since I wanted to limit the memory usage for one machine to 4GB, I should use the following:
{max_memory, 64}
The reason is that the ring_creattion_size is 64 which means there are 64 vnodes on my single test server.
64MB * 64 = 4096MB
After I changed max_memory to 64, riak is happy, and it didn't crash when I tried to load 20MM records.
Some interesting things I noticed:
1. since Riak use LRU for memory_backend, the old records are evicted if max_memory can't hold all records.
2. With the key as "70f21766-1cde-38d4-5920-a380003723b3", and value as "1365720608095#TQB:1.4:2:1",
4GB memory with 64 vnodes can hold about 2.5MM records
4GB memory with 4 vnodes can hold about 7MM records
Seems the number of vnodes/machine has big overhead
Thursday, February 14, 2013
eclipse JUNO hangs on start up
I use Eclipse JUNO every day. However, I couldn't start it today after I restart my Mac. Mac updated with Microsoft 2011 so I have to reboot Mac machine. The strange thing happened: Eclipse got stuck. I manually killed the start up process several times, but it didn't work. Then I googled it, and found the solution from this post, and here is what I did:
rm $WORKSPACE_DIR/.metadata/.plugins/org.eclipse.e4.workbench/workbench.xmi Then I can start eclipse, and happy coding. Friday, December 7, 2012
my shell script cheat sheet
1. find the total line number of a fold for some files:
find test -iname *.java | xargs wc -l | tail -1
2. count # of files in each folder recursively
for t in `find . -type d -ls | awk '{print $11}'`; do echo "$t `find $t -type f | wc -l`" ; done > ~/count.txt
find test -iname *.java | xargs wc -l | tail -1
2. count # of files in each folder recursively
for t in `find . -type d -ls | awk '{print $11}'`; do echo "$t `find $t -type f | wc -l`" ; done > ~/count.txt
Thursday, November 1, 2012
Some svn commands
Create tag from trunk or branch:
svn copy http://svn.mydomain.com/repository/myproject/trunk \
http://svn.mydomain.com/repository/myproject/tags/release-1.0 \
-m "Tagging the 1.0 release."
The tag created is the snapshot of the trunk at the time the "svn copy" is executed.
To be more precisely, the revision # can be passed to "svn copy":
svn copy -r 12345 http://svn.mydomain.com/repository/myproject/trunk \
http://svn.mydomain.com/repository/myproject/tags/release-1.0 \
-m "Tagging the 1.0 release."
Merge from Trunk to a branch:
1. check out the branch (assume the path is /path/to/mybranch)
2. go to above folder
3. run the following commmand:
svn merge http://svn.mydomain.com/repository/myproject/trunk .
It will merge all changes from trunk to mybranch since last merge.
The above command is same as:
svn merge -rLastMergedRevision:HEAD http://svn.mydomain.com/repository/myproject/trunk .
View merge history:
"svn log" doesn't display the merge history. It only shows the merge commit:
svn log------------------------------------------------------------------------ r196402 | liz | 2012-11-01 10:39:13 -0700 (Thu, 01 Nov 2012) | 1 line Merging r196340 through r196401 ------------------------------------------------------------------------ r196340 | liz | 2012-10-31 14:52:06 -0700 (Wed, 31 Oct 2012) | 1 line development branch for new feature
If need to see the merge history, the option --use-merge-history (-g) can be used with svn log:
svn log -g------------------------------------------------------------------------ r196402 | liz | 2012-11-01 10:39:13 -0700 (Thu, 01 Nov 2012) | 1 line Merging r196340 through r196401 ------------------------------------------------------------------------ r196388 | xyz | 2012-11-01 09:50:28 -0700 (Thu, 01 Nov 2012) | 2 lines Merged via: r196402 Added new unit tests ------------------------------------------------------------------------ r196340 | liz | 2012-10-31 14:52:06 -0700 (Wed, 31 Oct 2012) | 1 line development branch for new feature
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