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nexedi
gitlab-ce
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9492b5c0
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9492b5c0
authored
Jul 02, 2020
by
Thong Kuah
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Edit ordering_table_columns.md, move important info first
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doc/development/ordering_table_columns.md
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# Ordering Table Columns in PostgreSQL
For GitLab we require that columns of new tables are ordered to use the
least amount of space. An easy way of doing this is to order them based on the
type size in descending order with variable sizes (
`text`
,
`varchar`
, arrays,
`json`
,
`jsonb`
, and so on) at the end.
Similar to C structures the space of a table is influenced by the order of
columns. This is because the size of columns is aligned depending on the type of
the following column. Let's consider an example:
...
...
@@ -40,11 +45,6 @@ In these examples, the `id` and `user_id` columns are packed together, which
means we only need 8 bytes to store _both_ of them. This in turn means each row
will require 8 bytes less space.
For GitLab we require that columns of new tables are ordered based to use the
least amount of space. An easy way of doing this is to order them based on the
type size in descending order with variable sizes (
`text`
,
`varchar`
, arrays,
`json`
,
`jsonb`
, and so on) at the end.
## Type Sizes
While the
[
PostgreSQL documentation
](
https://www.postgresql.org/docs/current/datatype.html
)
contains plenty
...
...
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