Mail (MX) Server Survey

Exim приятно удивил.

http://www.securityspace.com/s_survey/data/man.202106/mxsurvey.html 

Server Type	Number of Servers	Percent
Exim	293,104	61.58%
Postfix	150,056	31.53%
Sendmail	16,869	3.54%
MailEnable	9,561	2.01%
MDaemon	2,337	0.49%

Postgresql storage alignment

 

https://www.postgresql.org/docs/current/catalog-pg-type.html

typalign char typalign is the alignment required when storing a value of this type. It applies to storage on disk as well as most representations of the value inside PostgreSQL. When multiple values are stored consecutively, such as in the representation of a complete row on disk, padding is inserted before a datum of this type so that it begins on the specified boundary. The alignment reference is the beginning of the first datum in the sequence. Possible values are: c = char alignment, i.e., no alignment needed. s = short alignment (2 bytes on most machines). i = int alignment (4 bytes on most machines). d = double alignment (8 bytes on many machines, but by no means all).

typstorage char typstorage tells for varlena types (those with typlen = -1) if the type is prepared for toasting and what the default strategy for attributes of this type should be. Possible values are: p (plain): Values must always be stored plain (non-varlena types always use this value). e (external): Values can be stored in a secondary “TOAST” relation (if relation has one, see pg_class.reltoastrelid). m (main): Values can be compressed and stored inline. x (extended): Values can be compressed and/or moved to a secondary relation. x is the usual choice for toast-able types. Note that m values can also be moved out to secondary storage, but only as a last resort (e and x values are moved first).

"Column Tetris"

CREATE TABLE t (

    e int2    -- 6 bytes of padding after int2

  , a int8

  , f int2    -- 6 bytes of padding after int2

  , b int8

  , g int2    -- 6 bytes of padding after int2

  , c int8

  , h int2    -- 6 bytes of padding after int2

  , d int8)

To save 24 bytes per row, use instead:

CREATE TABLE t (

    a int8

  , b int8

  , c int8

  , d int8

  , e int2

  , f int2

  , g int2

  , h int2)   -- 4 int2 occupy 8 byte (MAXALIGN), no padding at the end

As a rule of thumb, if you put 8-byte columns first, then 4-bytes, 2-bytes and 1-byte columns last you can't go wrong.