Intro

Report the size of each database, and how much is in regular tables, TOAST, and indices.

Report storage size per column as well (without the regular/TOAST split).

WARNING: sooooo, I misunderstood what each function does exactly, and the reports were significantly off. Update pending.

Example

 # pg_sizes
      'dataplot'  total size:   16MB, of which    table 12.7MB    toast  459KB    indexes  2.5MB    other  8.2KB
         'music'  total size:  5.1GB, of which    table  3.1GB    toast  1.1GB    indexes    1GB    other   33KB
        'quotes'  total size:  6.4MB, of which    table  2.8MB    toast  492KB    indexes  3.1MB    other     0B
         'solar'  total size:  537MB, of which    table  348MB    toast  459KB    indexes  189MB    other     0B
 Total size of databases: 5.7GB


# pg_sizes -d quotes -c -p
TABLE 'quotes'.'quotes'
  base table size      631K
       TOAST size       41K
       index size      737K
Number of rows: 3156
  NAME                              TYPE      DISK_SIZE                DISK_AVG     DATA_SIZE      DATA_AVG   COMPR
  quote                             text         432179 (   0 MB)         136.9        426875         135.3    101%
  quoter                            text          31937 (   0 MB)          10.1         28781           9.1    110%
  source                            text          16492 (   0 MB)           5.2         13324           4.2    123%
  viewed                         integer           6240 (   0 MB)           4.0
  proposed                       boolean
Total size of databases: 8.7MB

Where the last few columns are there to point out something similar to disk use versus apparent size.

which is different mainly due to overheads and TOAST compression
DISK_SIZE is space taken on disk (via pg_column_size)
DISK_AVG is that divided by row count
DATA_SIZE is the total uncompressed size (via octet_length, only applies to some types)
DATA_AVG is that divided by row count
COMPR is DISK_SIZE / DATA_SIZE to show overheads, and possible TOAST compression

Options

Usage: pg_sizes [options]

Options:
  -h, --help            show this help message and exit
  -d DBSUBSTR, --dbname-substring=DBSUBSTR
                        Only report databases containing given substring. Can
                        supply multiple with commas.
  -p, --precise-rowcount
                        By default we get the row count estimate via VACUUM
                        statistics, which can make the column sizes a little
                        imprecise. This forces a count(*), which is slower but
                        precise.
  -c, --column-sizes    Estimate size use per column. NOTE: this basically
                        reads all data, so is slow and will mess with your
                        caches
  -t TABSUBSTR, --table-substring=TABSUBSTR
                        Only show column sizes for tables containing given
                        substring. Can supply multiple with commas.

Notes

The database summary comes entirely from data in pg_class for each database.

The column stuff uses pg_column_size and octet_length, and some assumptions about how those relate to TOAST and indices, which is probably at least part of why they seem a little different.

Caveats

It looks like pg_class isn't always updated on vacuums, so this may be significantly off (after bulk inserts?).

Proof of concept version, contains various hardcoded assumptions. I still need to reread the docs on the various size functions to ensure it means precisely what I think it means.

The column summaries need to read a lot of table data. Which is slowish, and for databases larger than RAM will probably shred your nicely warmed caches.

Needs access to each database, so:

assumes we connect as postgresql role postgres
assumes that's trusted on localhost via pg_hba (so no username)
assumes that's the admin and can read everything

Also, you're running someone else's code on your database.

TODO / CONSIDER

Make the distinction of disk use versus data size in more places
maybe don't count on pg_class (used only for the overview) being correct - it can be off by a ''lot'' until the next vacuum
Output as JSON, or something else parsable
A 'forced index warming' mode or such, because we have code that matches filenames to relations so it wouldn't be a stretch to have
It may be useful to show disk use rather than apparent size, by stat()s to the filesystem. The code for it is commented out because it has to assume you have filesystem permissions, which is a point of failure you don't have using pg_class.
Clean up code, do some things more properly.

License

knobs-dials/pg_sizes

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