Question 239090 in PostgreSQL Question posted in
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Estimating PostgreSQL Table Size in GB for Varying Column Count and Row Quantity

I need to estimate the size in GB of a table in a PostgreSQL database. I don’t have the database yet (I need the estimate for cost projection purposes).

The schema of the table will be:

  • One column containing a timestamp of when the record was created
  • K other columns, all float numbers

K can be anywhere between 10 and 10000.

Is there a formula to estimate how big the table will be in GB, as a function of K and of the number of rows?

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2

Answers


  1. 0

    You could perhaps use this formula:

    Estimated Table Size (in bytes) = (Number of Rows) * (Size of
    Timestamp Column + (K * Size of Float Column))

    In PostgreSQL, the size of timestamp data type is generally 8 bytes. Float is 4 bytes.
    This formula however does not factor in null values, padding, alignment, compression, or indexing which could increase the size.

    You could also use the pg_total_relation_size function in PostgreSQL. You provide the function with the table’s name and it gives you the size of the table, including indexes and associated objects.

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  2. 0

    a tiemstamp needs 8 bytes

    A real 4 Bytes

    So you have 8+ K * 4 bytes of raw data

    lets say for 10

       23   -- heaptupleheader
 +  1   -- padding or NULL bitmap
 + 40   -- 10 * ireal
 +  8   -- padding after 3rd integer
 +  8   -- timestamp
 +  0   -- no padding since tuple ends at multiple of MAXALIGN
 +  4   -- item identifier in page header
------
 = 84 bytes for every row

    which ar 8.400000000000001e-8 Giagbyte, kow you need to estmate the rows you have prer month or year and multiple it

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