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Hi,

As far as I know, in SAW SQL Anywhere 17 and below it can be a maximum of 13 table spaces (1 main and 12 additional).

Question: Why is there such a restriction ? Why can there be 13 table spaces, and not say 255 ?

asked 15 Jan, 02:23

Stalker's gravatar image

Stalker
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Page IDs are 32 bits. 4 bits of a page id identify the dbspace: 13 for table dbspaces plus log, map, and temp files (16 files). The map file isn't used anymore -- it was used by the 'write file' feature that allowed updates to read-only dbs (ex, dbs on CDROM).

The remaining 28 bits are used as the physical page number within the file which gives (2^28)*page_size as the max dbspace file size.

If we allowed more files while keeping 32-bit page IDs, the size limit for each file would be smaller. Changing to larger page IDs (64-bits) would cost space on every page where we store page IDs and would be a very big, fundamental format change.

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answered 15 Jan, 08:55

John%20Smirnios's gravatar image

John Smirnios
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accept rate: 37%

Your answer is clear (thanks for such a detailed answer), although 13 tablespaces are still not enough.

Can You tell me whether You have plans to increase the bit size of this identifier (48 or 64 bits) ?

(16 Jan, 01:59) Stalker

Perhaps it would be useful if you could explain why you think you need more than 13 tablespaces?

(16 Jan, 03:30) Mark Culp

The map file isn't used anymore.

So, technically, you could increase the number of allowed additional dbspaces from 12 to 13? (Note: I don't have that need.)

(16 Jan, 05:34) Volker Barth

I store document tests (files) in my database, so the database is growing quickly. Now my database page size is 16 kb, I don’t want to increase it to 32 kb or store document texts outside the database.

In my opinion, it’s better to have two 4 TB table spaces than one 8 TB table space - it’s easier to operate with smaller files

(18 Jan, 01:55) Stalker
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So, given you can have 13 dbspaces with at maximum 4 TB for 16 KB pages, are you facing a 52 TB database size limit? Just out of curiosity: How long does a backup (and a restore) take?

(18 Jan, 03:28) Volker Barth

In a week, users retain on an average of 15 GB in the database of texts of documents. I can fill each table space no more than 75% of its size (this is necessary so that there is still a place to change the file previously saved there). I am still far from filling all the tabular spaces, now the total volume of the base (all the database files except the log) is about 5 TB, but I look into the future and if there was no such restriction on tabular spaces, it would be easier for me.

As for the backup, an incremental backup is made.

(19 Jan, 05:25) Stalker
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question asked: 15 Jan, 02:23

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last updated: 19 Jan, 05:25