I would like to know how do i convert number of row into size like in MB or KB?
Is there a way to do that or formula?
The reason I doing this is because I would like to know given this set of data but not all in tablespace, how much size is used by this set of data.
Thanks,
keith
If you want an estimate, you could multiple the row count with the information from user_table.avg_row_len for that table.
If you want the real size of the table on disk, this is available user_segments.bytes. Note that the smallest unit Oracle will use is a block. So even for an empty table, you will see a value that is bigger tzen zero in that column. That is actual size of the space reserved in the tablespace for that table.
Related
I´m working with PostgreSQL. I have a database named db_as on it with 25.000.000 rows of data. I wanted to set some diskspace free so I updated a full column to null value thinking that I would decrease databases size, but it didnt happend, in fact, i did the oposite thing, I increased databases size, and i dont know why. It increased from 700MB to 1425MB, thats a lot :( .
I used this sentence to know each columns size:
SELECT sum(pg_column_size(_column)) as size FROM _table
And this one to know all the databases size:
SELECT pg_database.datname, pg_size_pretty(pg_database_size(pg_database.datname)) AS size FROM pg_database;
The original values will still be on disk, just dead.
Run a vacuum on the database to remove these.
vacuum full
Documentation
https://www.postgresql.org/docs/12/sql-vacuum.html
A DB2 / 400 SQL question: In the statement below, when creating a column with the "ALLOCATE"
statement, does this mean that the database engine creates the column with an initial size of 20 Mega?
Because the analysis of the system table indicates that the column with a column of 2G, 7M.
Does the size indicated in the "LENGHT" column correspond to the size allocated, or to the maximum size of the column ?
Db2 for IBM i stores table data in two parts.
The Fixed length row-buffer table space and an overflow space.
If a table just has fixed length columns, all the data is in the table space.
ALLOCATE(x) means that the Db allocates x bytes in the table space for the column and the rest is stored in the overflow space.
The default for varying types is allocate(0), so theoretically the entire varying value is store in the overflow space.
Reality is varchar(30) or smaller is stored in the fixed length table space for performance, unless you explicitly specify allocate(0).
The reason it matters, if a query access both the fixed length table space and the overflow space, then 2 I/Os are required to retrieve all the data.
IBM recommends using an allocate(x) where x is large enough to handle at least 80% of values you have.
As you can see for yourself, length is the maximum size for the column.
IBM ACS's schema tool, for one example, shows you the allocated length...
create table mytable (
mykey integer
, myclob clob(200000) allocate(2000)
);
Assuming I have a table in PostgreSQL, how can I find the exact byte size used by the system in order to save a specific row of my table?
For example, assume I have a table with a VARCHAR(1000000) field and some rows contain really big strings for this field while others really small. How can I check the byte size of a row in this case? (including the byte size even in the case TOAST is being used).
Use pg_column_size and octet_length.
See:
How can pg_column_size be smaller than octet_length?
How can I find out how big a large TEXT field is in Postgres?
How can pg_column_size be smaller than octet_length?
I'm executing a SQL query that joins 100+ tables together and I am running into the following error message:
Cannot create a row of size 8131 which is greater than the allowable
maximum row size of 8060.
Just would like to know what my options are at this point? Is this query impossible to execute? Are there any workarounds?
Appreciate any help
Thanks
Your problem is not the join, or the number of tables. It is the number and size of the fields in the SELECT. You are reaching a row size limit, not a row count limit.
Make sure you are not using any "*" in your SELECT, then eliminate any unused fields and trim/limit strings where possible.
From MSDN forum:
You're hitting SQL's row size limit which is 8060 bytes (eg an 8K page). Using normal data types you cannot have a row which uses more than 8060 bytes, and while you can use a varchar to allow the smaller bits of data to offset the larger ones, with 468 columns of data you're looking at an average column width of 17.2 bytes.
If you convert varchar(x) to varchar(max) issue will be resolved.
Please also refer: How SQL server stores of the size of the row is greater than 8060 bytes Difference Between varchar(max) and varchar(8000)
let's say I have a column on my table defined the following:
"MyColumn" smallint NULL
Storing a value like 0, 1 or something else should need 2 bytes (1). But how much space is needed if I set "MyColumn" to NULL? Will it need 0 bytes?
Are there some additional needed bytes for administration purpose or such things for every column/row?
(1) http://www.postgresql.org/docs/9.0/interactive/datatype-numeric.html
Laramie is right about the bitmap and links to the right place in the manual. Yet, this is almost, but not quite correct:
So for any given row with one or more nulls, the size added to it
would be that of the bitmap(N bits for an N-column table, rounded up).
One has to factor in data alignment. The HeapTupleHeader (per row) is 23 bytes long, actual column data always starts at a multiple of MAXALIGN (typically 8 bytes). That leaves one byte of padding that can be utilized by the null bitmap. In effect NULL storage is absolutely free for tables up to 8 columns.
After that, another MAXALIGN (typically 8) bytes are allocated for the next MAXALIGN * 8(typically 64) columns. Etc. Always for the total number of user columns (all or nothing). But only if there is at least one actual NULL value in the row.
I ran extensive tests to verify all of that. More details:
Does not using NULL in PostgreSQL still use a NULL bitmap in the header?
Null columns are not stored. The row has a bitmap at the start and one bit per column that indicates which ones are null or non-null. The bitmap could be omitted if all columns are non-null in a row. So for any given row with one or more nulls, the size added to it would be that of the bitmap(N bits for an N-column table, rounded up).
More in depth discussion from the docs here
It should need 1 byte (0x00) however it's the structure of the table that makes up most of the space, adding this one value might change something (Like adding a row) which needs more space than the sum of the data in it.
Edit: Laramie seems to know more about null than me :)