19 replies to this topic

[Ross Bevin]

The maximum ProISAM file size is 384MB. To create a file that can expand to the maximum you need to create it using the following command. This example has a key length of 24.

iscr32.exe -k24 -r3000 test.pro

[Joseph Bove]

Guest,

You may need to check the record length to find the file size.

To do this use the iskeys32 utility.

iskeys32 filename.pro | more

record length: will appear right near the top.

hth,

Joseph

[Chris Pepper]

Personally I use the -s option on iskeys to set a start key past the last key on the file.

So I gues we all have our own methods!!!

[Joseph Bove]

Guest,

When your problem is maximum file sizes you probable don't
want to do iskeys on the file - much simpler to look at the
Pro-IV definition... That goes for 'more' too - look into
'head' and 'tail' unix commands

As far as I know, there is no way to determine the maximum file size of a ProISAM file by looking at the file definition. The reason is that when the file is created, any record length may be specified. It is the record length at file creation time that determines the maximum size of the file...

The record length recorded within ProIV is just the total number of bytes per record.

Regards,

Joseph

[Joseph Bove]

Guest,

The -r option doesn't really set a record size at all, it determines the BLOCK size of the ProISAM file and hence determines the max file size.

This is my understanding too. We have a special tool for our Unix clients that relies on the information from iskeys to determine what the actual maximum file size is. This is then compared to the actual file size and a percentage of use calculated.

Then, to make things very easy for the client, a report is generated if any files are over 80% of capacity. This has saved us a number of crashes and emergencies since we implemented it.

Unfortunately, we've not built the same for Windows or I'd gladly share it.

Regards,

Joseph

[Chris Pepper]

OK, a quick history lesson on why Pro-Isam exists at all.
When ProIV was first put on the PC it used C-Isam. In the begining under PC-DOS a program was restricted to using just a few file-handles (16 or 32 or something like that). Since C-Isam needs 2 per file this meant that ProIV pretty much ran out of files using the files needed for Run-time, let alone development. So a programmer quickly put together a simple B-tree file system that stored both the index and data in a single file thus doubling the number of files that could be accessed.

Since the amount of storage was effectively limited by the hardware available at the time, accessing huge amounts of data wasn't a requirement.

ProIsam was just one of those accidents of history.

The basic design limits the number of blocks, so increasing the block size is the only way to increase the overall file size.

I agree with Joseph that 80% is a good "warning level". In the past I've noticed that, probably due to the way the B-tree grows that a file can suddenly grow at a much faster rate as more records are added. Clearly it depends on the spread of the keys.

[Dan Shannon]

Just an unreasonable opinion based on nothing but snobbery:

The maximum size for a PRO-ISAM file in any self-respecting production application ought to be 0 bytes.

I'm in a bad mood, sorry.

[Donald Miller]

So is it still true that Pro IV is more efficient, if the record size is large, that you keep the whole record within one block ?

ie. if the record size is 600 bytes and the block size 500 then re-creating the file with a larger block size will keep things efficent.

Does the block size have to be a factor of 8/16/64 ?

Cheers

[Joseph Bove]

Dan,

The maximum size for a PRO-ISAM file in any self-respecting production application ought to be 0 bytes.

That creates quite a burden for logic.pro and genfile.pro!

Regards,

Joseph

[Mike Schoen]

I got these numbers from pro-iv years ago, when we had some proisam files explode.

Page Length Maximum Size
----------- ------------
512 32MB
1024 64MB
1536 96MB
2048 128MB
2560 160MB
3072 192MB
6144 384MB


We have written a global function to always create files with a page size of 6144 (equivalent to iscr -kN-e 3000),
and we run scripts unix systems to parse ischk -v output and warn of file size issues based on these numbers.

Doesnt help if a customer ignores the report, but enough people catch it to make it worthwhile.

[Chris Pepper]

So is it still true that Pro IV is more efficient, if the record size is large, that you keep the whole record within one block ?

No, a requirement of ProIsam is that you must always be able to get at least 2 records in a block. AFAIK you will get an error message if you try to write a record larger than a block. ProIsam cannot cope with 'block spanned records'.