PostgreSQL Datatypes

SQL datatypes and internal datatypes

SQL type	Internal type
smallint	int8
int	int32
bigint	int64

PostgreSQL : Get total pages of an object

SELECT pg_relation_size(<object_id>, 'main')/8192);

The pg_relation_size gives the disk space occupied by the object. Since each page is of 8kB, the pg_relation_size size is divided by 8192 to give the page count.

Vim - Highlight OverLength

Add the following code to /etc/vimrc if we want to highlight the characters that go beyond column 80.

highlight OverLength ctermbg=red ctermfg=white guibg=#592929

match OverLength /\%81v.\+ 

PostgreSQL : Data Object sizes

 Size of User Tables

=# SELECT
   relname as "Table",
   pg_size_pretty(pg_total_relation_size(relid)) as "Total Size",
   pg_size_pretty(pg_relation_size(relid)) as "Relation Size",
   pg_size_pretty(pg_total_relation_size(relid) - pg_relation_size(relid)) as "External Size"
   FROM pg_catalog.pg_statio_user_tables ORDER BY pg_total_relation_size(relid) DESC
;
      Table       | Total Size | Relation Size | External Size
------------------+------------+---------------+---------------
 load_test        | 1883 MB    | 1776 MB       | 107 MB
 pgbench_accounts | 1121 MB    | 961 MB        | 161 MB
 pgbench_history  | 8656 kB    | 8656 kB       | 0 bytes
 pgbench_tellers  | 80 kB      | 40 kB         | 40 kB
 pgbench_branches | 24 kB      | 8192 bytes    | 16 kB
(5 rows)

 Size of User Indexes

=# SELECT
   indexrelname as "Index",
   pg_size_pretty(pg_total_relation_size(indexrelid)) as "Size",
   pg_size_pretty(pg_total_relation_size(indexrelid) - pg_relation_size(indexrelid)) as "External Size"
   FROM pg_catalog.pg_statio_user_indexes ORDER BY pg_total_relation_size(indexrelid) DESC;
         Index         |  Size  | External Size
-----------------------+--------+---------------
 pgbench_accounts_pkey | 161 MB | 0 bytes
 load_testidx          | 107 MB | 0 bytes
 pgbench_tellers_pkey  | 40 kB  | 0 bytes
 pgbench_branches_pkey | 16 kB  | 0 bytes
(4 rows)

 Functions

pg_relation_size(oid) - returns disk space occupied by the table or index of the given oid.

pg_total_relation_size(oid) - returns total disk space of the table of given oid, including indexes and toasted data

Clearing OS cache

Run the following command as root

echo 3 > /proc/sys/vm/drop_caches

Adding libpq in Contrib module

To include libpq functions in the contrib module the following header should be included:

#include "libpq-fe.h"

However, it throws the following error:

error: libpq-fe.h: No such file or directory

This can be solved by including the following in Makefile of that contib

PG_CPPFLAGS = -I$(libpq_srcdir)

This includes the option -I../../src/interfaces/libpq during make and hence the header file becomes accessible. 

gdb commands

Future breakpoints

Set break point on future shared library:

set breakpoint pending on

Debug fork

To hold the forked process by gdb and not allow it to run independently:

set detach-on-fork off 

Vim - Change case

Open the document in vim, press v and move to select text and then press one of the following:

U - converts to upper case
u - converts to lower case
~ - toggles the case of selected

To change text of entire file to lower case run the following

ggVGu

replace u with U for uppercase and ~ to toggle.

Postgresql - Set timing on by default

For the psostgres user create file in the home folder:

vim ~/.psqlrc

and add the following to the file

\timing

When you connect to database and run  a query, the time is also displayed:

postgres=# SELECT current_timestamp;
               now              
----------------------------------
 2014-03-11 10:34:40.378455+05:30
(1 row)
Time: 43.821 ms

Vim - Replace with incremental value

:let @a=1 | %s/<old_word>/\='<new_word>'.(@a+setreg('a',@a+1))/g

If the <old_word> is replaced with abc
and <new_word> with xyz

:let @a=1 | %s/abc/\='xyz'.(@a+setreg('a',@a+1))/g

The command will replace all abc with xyz.<number>. The <number> will start with 1 and increment by 1.

1st abc will be replace by xyz.1
2nd abc will be replace by xyz.2
.
.
.
so on

Find the list of directories with their Sizes

Get Size of all sub-directories

Command: 

du -sh <directory_path>/*

Example:
$ du -sh /home/Beena/*

4.0K /home/Beena/Desktop
4.0K /home/Beena/Documents
64M /home/Beena/Downloads
4.0K /home/Beena/Music
4.0K /home/Beena/Pictures
4.0K /home/Beena/Public
4.0K /home/Beena/Templates
4.0K /home/Beena/Videos

Get all files and sub-directories More than a specified size

Command: 

find <dir_path> -size +<size> -ls

Example:
$ find /home/Beena/ -size +10M -ls

Get all files and sub-directories Less than a specified size

Command: 

find <dir_path> -size -<size> -ls

Example:
$ find /home/Beena/ -size -10M -ls