Wednesday, December 07, 2016

Unexpected feature

I have a task to experiment with 2 instances of InterBase XE7 at the same computer.
Install went OK over existing instance gds_db. Don't forget to specify "Multi instance feature" = YES and new port name and number at the second dialog of installer.

Well, first of all, after running 2 instances of InterBase XE7, one at gds_db/3050, another at gds_db/3100, I decided to check do they ever work by connecting to the same database.

You know, SuperServer is one process, that opens database for itself, and none others. So, theoretically (and in previous versions) it locked database file using exclusive access, to avoid file corruption by modifying it with concurrent processes.

Ok, but both instances were able to connect to one DB at the same time! What the crap? Looking into monitoring tables (tmp$) I found that second instance (second connect) show only 1 record in tmp$attachments, while first show 2 records (one of them garbage collector).
Mmm... Then I came to an idea that second instance connected in read-only mode. Tried to update some data, and ...

The insert, update, delete, ddl or authorization statement cannot
 be executed because the transaction is inquiry only.
attempted update on read-only database.


Well, I got the idea but did not understand the purpose. Because the instance that connects to the database first will get read-write access, and second - read-only. But there are none options that can set "read-only mode for instance x". So, wins the first one?
For me it seems completely useless and even dangerous in production - unpredictable first connection from the wrong instance can lock DB (read-only) for the main instance. The better way, I think, was to lock DB in exclusive mode. At least, it can show at connect time that someone already opened DB by some another instance.

Friday, September 02, 2016

Incompatible Compatibility

As you know (maybe), InterBase XE7 have support of previous ODS (database format) of InterBase 2009 (ODS 13) and InterBase XE/XE3 (ODS 15).
This, I think, was supposed to help moving to XE7, starting to use XE7 with old databases, and "if something goes wrong" to have an ability to return to 2009 or XE/XE3.

But...

InterBase XE7, when opens database in ODS 13.1 format (InterBase 2009) upgrades it's minor version to 13.2. And after that InterBase 2009 can not open this database anymore. Because it supports 13.1, not 13.2. Oops. Incompatible.
So, support of ODS 13 by XE7 seems useless?

Tuesday, June 07, 2016

Mess of gbak options

I see lot of places where gbak options (Firebird, InterBase) specified randomly.
Examples:
gbak -c -r

what do you mean? -c or -r? Documentation specifies -c | -r. Symbol "|" is OR, not AND. Moreover, -r is not restore, it's REPLACE!
Thanks god, Firebird 1.5 and higher disabled -r option, because it allow to drop original database file without warning. Now you must specify -rep or -r o. Anyway, both of these is useless, because -c is enough. If you write script, rename original file before gbak -c. If something went wrong, you will have original DB file safe.

gbak -t ...
Come on, -t is default option for transportable backup. You think that someone will change it later to non-default? I doubt so.


gbak -c ... -page_size ...
don't incude this to regular script. Page size change usually made once, by administrative decision. If you specify this option in the script, and there is 4096 specified, after changing page size to 8192 and regular restore you will get 4096 again. Leave -page_size option to manual change.

gbak -b ... -ig ...
Ignoring checksum errors is useful only when database is corrupted. If you include this option to regular script, you may not find that database is broken.

p.s.
45 Ways To Speed Up Firebird Database
12 Common Mistakes while Backing Up Databases
HQbird: advanced Firebird SQL for Enterprises




Saturday, April 23, 2016

Delimiter hell

You know, that each computer can have different regional settings. Moreover, some users change this settings to their preferences.
For example, if I like '.' as decimal separator, I can change it, if by default it is ','.

But, we are speaking here about Firebird and InterBase, right? Yes. There is a tool, GSTAT, used to get statistics from DB. It uses fixed decimal separator, '.'. So, if you run gstat -r employee.gdb, somewhere in the file there will be lines

COUNTRY (128)
    Primary pointer page: 407, Index root page: 408
    Average record length: 26.00, total records: 14, max record length: 31

You see "26.00" ? Right, here dot is used as delimiter, and it's being used forever, and system settings are ignored.
But, someone in Embarcadero, working on new InterBase version, decided to use system delimiter for Services API. So, if we will try to get statistics not by gstat, but by services API, we can get

    Average record length: 26.00, total records: 14, max record length: 31
or
    Average record length: 26,00, total records: 14, max record length: 31

I don't know why and when this happened. But I found this only few hours ago...

Wednesday, October 10, 2012

Don't miss Firebird Conference!

Only 15 days left before Firebird Conference, Luxembourg, 26-27 October.
Unique chance to handshake Firebird developer team, drink beer/wine during evening gathering, and, of course, to learn lot of interesting things about Firebird and application development!

http://firebirdsql.org/en/firebird-conference-2012/

Read the topics list, speaker names, and join us!

Tuesday, September 06, 2011

Operating system on RAID

We deal with the hardware by lot of different cases - when someone ask us what to buy for the new server, how to improve existing hadware, and, of course, when database becomes corrupted.

Many hadware vendors (as we see) sell servers with ready to use RAID (1, 5 or 10), with operating system installed on that raid. Also these hardware vendors think that it is cool that customer will place everything else on that RAID, and it will work perfectly (long and stable), so, no additional disks. That common mistake leads to real pain if something happens with the RAID.

Well, if you had your database on the RAID, and it fails, you need to find latest backup, and restore from it (after repairing RAID, of course).
But, if there were operating system on that RAID, it becomes a bit more complicated.

10 minutes ago we had a request to repair database from the RAID, broken by it's controller fail. The database is a real mess, so, sorry, there is nothing left to repair.
I don't know, was there also operating system, or not, but if it were:
- Your server failed, and it can't boot. You can't understand what happened with RAID.
- You need to attach additional HDD to server, install operating system on it, boot, then install RAID drivers and RAID software.

How much time it will take?
Well, let's put operating system on separate drive. RAID failed? Well, ok, but we can boot and look at RAID state.
You have doubts about that hard drive reliability? Make image backups. OS does not occupy much space - such an image can be stored even on flash-drive.

Ok, someone will say - yes, I will separate OS and my data. But I still want to keep OS on RAID 1, for reliability. Of course, it will protect OS from single disk failures, but, if RAID controller will fail, we will be at the starting point of that story.

Thus, my opinion is to have cheap (or not) and one (!) HDD for OS, that can be changed in a few minutes, and can be bought in any computer store nearby.
This solution, in spite of cheapness, can save lot of time in case of failure.
Think about it. Don't rely on "cool expencive RAID". Be a bit paranoid. :-)

Wednesday, March 23, 2011

no_garbage_collect

You do not know what is that? Well, InterBase and Firebird allow specifying connection parameter that will disable garbage collection by statements in this connection.
This is the same as the option -g for gbak. And, of course, all other connections without this parameter will continue to try collecting garbage in the database, if any.

This connection option mostly is not known, because standard and "closed source" drivers usually does not produce access to server-specific features. Thus, you may use this option only for IBX (IBExpress components in Delphi and C++Builder), FIBPlus, and some other "direct access" components. ODBC, dbExpress? No, of course.

But, why you may ever need this option?
Sometimes you may want to run huge report that will scan lot of data. And, at the moment this report will run, there may be lot of garbage record versions in the database. So, your report connection will collect garbage (especially if you use Firebird Classic), and report will run much slower than it could be.
In this case, before running the report, you may set no_garbage_collect option, and report will be fast as a rocket.

I also knew some small applications with small databases (up to 1gb), that used no_garbage_collect option for all connections. This way garbage is not collected at all, and during the day size of database could grow 2 or 3 times. But, each day database was scheduled to backup and restore, so, why to care about garbage?

Since I do not see needs to do backup and restore each day, I do not recommend disabling garbage collection this way. Use it only for specific connection, if you ever need to do this at all.