I've seen the following terms used:
wide field – e.g. "the TOAST mechanism first attempts to compress any wide field values"
wide column – e.g. "If you have many wide columns" or "even complete toasting doesn't allow a row with more than about 450 wide columns".
But I haven't seen them defined.
I understand Posgres has a page/block size limit (typically of 8192 bytes) and that it will rely on TOAST when the data doesn't fit within the limit. But, as I understand it, this is based on the size of the row, not on the size of any one column. So I understand how one could say a row to be wide… but a particular column? (But maybe I'm taking this too literally.)
In this context, what's the threshold for considering a column to be wide?
Related
In a 3-level paging system, when every page size is 512 bytes and an entry size is 4 bytes, we can know that every single page has 128 entries. So we can design 7 bits (log128) of the VPN(Virtual Page Number) as an index in the third level page table, which makes the page table fit perfectly in a page. What happens if we just design 6 bits as an index? I think on third level page table, some pages could not be correctly "transfer" to corresponding physical frame number because their page number can not be represented by a six-digit index. For example, when the OS "cut" the whole page table into 3 parts, each of which has 128 entries, and one entry happens to be the 100th entry of second part. How can we use 6 digits to index into 100 to get the right frame number in physical address? Or the "cut" process is smart enough to put just 64 entries and waste another 64 entries in every page? Or we actually can use 8 digits to index into 128 entries table, using just 7 digits and ignore one digit? This problem really confuses me a lot because even if the third level page table perfectly fits into one page, the first and the second level page table sometimes do not fit perfectly at all.
I got the answer from Stack Exchange and here is the same question https://cs.stackexchange.com/questions/103454/what-does-it-mean-the-outer-level-page-table-need-not-be-page-aligned.
We have to do some analysis on some tables for that we have to find out the maximum possible row size of each table in db2 db.
Please let us know..
Check out the Db2 documentation for CREATE TABLE. It contains the lengthy formula to compute the row size for a table. It depends on many attributes like
the type of table,
the column data types,
if they allow NULL,
if value compression is enabled,
...
The maximum possible row size depends on the page size, but there is also a column count limit.
If you don't need it precisely, you can sum up the byte count for each column data type in your table, add some extrac bytes. Then, make sure it is below 1/4 of the page size.
The Q Webserver per default returns a limited view of n rows and has the option to scroll (up/down/start/end). Is there any way where I can remove that restriction and display the whole table/list/dict? Or at least increase n?
Using \C with two arguments, eg. \C 100 1000 (first for number of rows, second for number of columns) will adjust the console size to display more rows and columns. 2000 is the maximum limit for each dimension.
See the link below for further information too:
https://code.kx.com/q/ref/cmdline/#-c-http-size
.z.ph might be more useful for you if you need to work around the limit. See: https://code.kx.com/q/ref/dotz/#zph-http-get
Customising the webserver is another option for modifying the output to the screen. See:
https://code.kx.com/q/cookbook/custom-web/
Is there a limit on the maximum number of classes i can have in using ColumnDataClassifier? I have about addresses that I want to assign to 10k orgs, but i kept running into memory issue even after I set the -xmx number to maximum.
There isn't an explicit limit for the size of the label set, but 10k is an extremely large set, and I am not surprised you are having memory issues. You should try some experiments with substantially smaller label sets (~ 100 labels) and see if your issues go away. I don't know how many labels will practically work, but I doubt it's anywhere near 10,000. I would try much smaller sets just to understand how the memory usage is growing at the label set size grows.
You may have to have a hierarchy of labels and different classifiers. You could imagine the first label being "California-organization", and then having a second classifier to select the various California organizations, etc...
According to documentation
Maximum Columns per Table 250 - 1600 depending on column types
Ok, but if have less than 250 columns, but several they contains really big data, many text type columns and many array type columns (with many elements), then there is any limit?
Question is: there is any size limit for per row? (sum of all columns content).