Dariusz on Software

I got the following error:

ORA-00932: inconsistent datatypes: expected NUMBER got BINARY

on line:

<property name="customer" column="CustomerId" />

the fix for above error was to use many-to-many tag instead of plain <property>:

<many-to-one name="customer" column="CustomerId" />

Note that class is not required here - it's computed from return type of getCustomer() getter by reflection.

When you are joining to an existing project you don't have good knowledge of internal project structures. Existing documentation may be inaccurate or just missing. In this case you can rely only on clean source code structure and source code comments. Based on them you can generate API docs using Javadoc or Pydoc for instance. But what with persistent data model stored in database? SchemaSpy comes with help here!

SchemaSpy is small (~200kB) Java application that is able to render schema retrieved from JDBC connection into set of "hyperlinked" HTML pages with Java Script and (if GraphViz installed) diagrams. Below you see one page of example output of this tool:

Installation is very simple. I'll describe integration process with Eclipse. First: download jar with application. Then create new Run configuration in Eclipse:

Add downloaded jar to classpath:

Then fill execution program arguments. My preferred list is as follows:

-t orathin -db XE -u <db-user> -p <db-password> -o /opt/c2p/schema-docs -dp /opt/lib/ojdbc14.jar -host localhost -port 1521 -schema <db-schema> -noimplied

"orathin" option is database type and ojdbc14.jar contains JDBC driver for this connection type. "-noimplied" option will make documentation generation faster and saves some disk space for big projects.

The only missing feature for me is to disable rendering of attributes on diagrams (some association-rich tables gives very big images that could kill Firefox browser). It's an open source so I hope to fix this soon and of course release a path :-)

    <link>http://blog.aplikacja.info/blog/2009/09/16/monitor-heap-size-in-eclipse/</link>

A very useful feature introduced lately in Eclipse IDE is presentation of current environment heap size. You can check how your Eclipse usage changes memory used and this way you can optimize some processes. Monitor sits in right bottom corner of main window and additionally you have the possibility to manually run garbage collector (trash icon):

You can enable it on General Preference page:

By default Oracle is cryptic about details of an error. Directive SHOW ERRORS is very useful during debugging of stored procedures for instance.

Eclipse SQL Explorer is simple but powerfull tool to inspect Your database state. You can:

• exec SQL commands
• browse database objects in Eclipse (including existing indices)
• open multiple databases at once

Installation is pretty simple:

1. Download preferred version (select any sqlexplorer_plugin-*.zip file)
2. Unpack this ZIP to your Eclipse directory: unzip sqlexplorer_plugin-*.zip
3. Restart Eclipse

Usage: switch to SQLExplorer perspective and define new connection:

If needed driver is not on the list you have to configure new driver by selecting JDBC jar file from Your disk.

By default the following views are present in SQL Explorer perspective:

• Connection list
• SQL commands history
• SQL editor window
• Database details (table structure, indices are here)
• Database structure (list of tables, views etc.)

Enjoy!

The story

After few months with a2b2.com without VPS panel (see: HyperVM exploit story) i decided to say bye-bye and move my monitoring node to another host. I selected small company fivebean.com for this purpose.

First I thought about VPS but then saw few interesting options mentioned on shared hosting offer:

Ruby on Rails (FastCGI), PHP 5.2.9 (IONCube/Zend Optimizer), mySQL 5.0.67, Perl 5.8.8, Python 2.4.3, GD Graphics Library, ImageMagick 5+, CGI-BIN, SSI (server side includes), Trac, Subversion and more!

Looks like we have long running processes-friendly hosting! I asked them about rules and got the answer:

The CGI processes are executed by suexec and would run as the user (script owner). We currently do not have any process limitations on scripts but we do have scripts that monitor for high usage and in which case we work with the user to resolve. If you have any other questions please let us know.

Seems very interesting. I appreciate hosts that control resource usage (CPU/disk) because that lowers possibility of abusing all resources on a server by one customer. Good.

Offer

The offer is pretty good: $1.02/mo when paid for one year in advance. Compare it to Dreamhost: $8.95/mo* or Bluehost: $6.95/mo. The servers are in Chicago:

8. ae-72-72.ebr2.Frankfurt1.Level3.net       0.0%    53   43.1  43.3  41.8  54.0   2.2 ae-92-92.ebr2.Frankfurt1.Level3.net
9. ae-43-43.ebr2.Washington1.Level3.net     0.0%    53  141.8 142.6 139.9 153.2   1.8
10. ae-2-2.ebr2.Chicago2.Level3.net          0.0%    53  142.7 143.4 142.3 144.4   0.5
11. ae-5.ebr2.Chicago1.Level3.net            0.0%    53  142.7 146.6 141.0 155.5   4.6
12. ae-24-52.car4.Chicago1.Level3.net        3.8%    53  213.5 150.6 140.8 282.8  30.2
13. WBS-CONNECT.car4.Chicago1.Level3.net     0.0%    53  146.9 147.2 145.3 161.5   2.4
14. 208.79.234.18                            0.0%    53  161.6 167.9 160.5 295.5  20.2
15. 209.188.90.57                            3.8%    53  162.0 163.9 160.6 193.9   5.7
16. maui.fivebean.com                        0.0%    53  163.6 165.5 160.8 176.0   3.4

Ping is about 160 ms from Warsaw. Not bad.

I paid using PayPal and have running account in minutes.

Environment Details

I checked for limits under ssh:

$ ulimit -a
core file size          (blocks, -c) 200000
data seg size           (kbytes, -d) 200000
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 200704
max locked memory       (kbytes, -l) 32
max memory size         (kbytes, -m) 200000
open files                      (-n) 100
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 20
virtual memory          (kbytes, -v) 200000
file locks                      (-x) unlimited

Parameters that shows some restrictions relevant to me:

• Max memory size (RSS): restricted to 200 MB. It's okay for me because my scripts often use less than 20 MB of RSS
• Maximum open files: 100 concurrent opened descriptors - seems reasonable
• Maximum user processes limited to 20: it may influence multi threaded applications. Monitoring processes are started as separated threads, so I have to limit concurrent measurements accordingly
• Virtual memory: it may influence multi threaded applications with big stack size

I asked if max user processes could be raised but got the answer:

To maintain stability cpanel sets this limit as a hard value and unfortunately we cannot modify it at this time. We apologize for any inconvenience.

I discovered that no quota was configured on my account:

$ quota -v(no output)

Seems not all aspects of server are configured properly. Another issue is with SSH login time:

$ time ssh fb ls(...)
real    0m52.980s
user    0m0.032s
sys     0m0.012s

It's weird, another host with "Turbo" package seems to be much faster:

$ time ssh gamma ls(...)
real    0m2.505s
user    0m0.028s
sys     0m0.008s

Slow SSH connection states bolded out:

debug1: Next authentication method: publickey
debug1: Offering public key: /home/(...)/.ssh/id_rsa
debug1: Server accepts key: pkalg ssh-rsa blen 149
debug1: read PEM private key done: type RSA
debug1: Enabling compression at level 6.
debug1: Authentication succeeded (publickey).
debug1: channel 0: new [client-session]
debug1: Entering interactive session.

No idea what is broken (a network timeout somewhere)?

Another issue is random restarts. Apache is restarted from time to time. I suspect there's automated watchdog that kill processes that use too much resources, Here you can see more timing information from FastCGI process (Trac instance) on this machine. Below one week monitoring with 5 minutes interval result:

Support

Few things have to be adjusted by support ticket:

• SSH was disabled by default - they enabled it for me
• Crontab was blocked - it was enabled, too
• Few system Python-related libraries was missing - were added in minutes

I evaluate support quality as very good.

Panel

It's a regular shared hosting so you can use user-friendly tools like CPanel. It's classic tool for such task and is pretty intuitive in usage.

My presonal preference is shell, so I use it if possible (e.g. crontab edits).

Summary

So far, so good. You can check how this deployment is working under this address (It's a node from monitoring system site-uptime.net, BTW). I'll write more details about hosting after few months of usage.

VPS also is considered to be checked, I'll write more details after setup.

To sumarize:

• + cheap economical offer
• + Trac/Subversion out of the box
• - slow SSH login
• - frequent (few times a week) short (<few minutes) downtimes

Today I installed (again) Oracle XE on Debian (Lenny) and got the following error:

ORA-01034: ORACLE not available
ORA-27123: unable to attach to shared memory segment
SVR4 Error: 13: Permission denied

I suspected problem was caused by errant ORACLE_HOME / ORACLE_SID values bug got the answer:

chmod 6751 $ORACLE_HOME/bin/oracle

That gives "-rwsr-s--x". Why permissions were not set properly on installation - have no idea. Any clues?