On 12/15/2016 07:48 AM, Tom DalPozzo wrote:
2016-12-15 16:23 GMT+01:00 Adrian Klaver <adrian.klaver@xxxxxxxxxxx
<mailto:adrian.klaver@xxxxxxxxxxx>>:
On 12/15/2016 07:17 AM, Tom DalPozzo wrote:
Hi,
it's not clear to me when tuple data (max 1000 bytes total) get
compressed on disk and when not.
I tried with pg_column_size to find the tuple's size but I
get ambiguous
results.
What is the table definition?
Maybe this will help?:
https://www.postgresql.org/docs/9.5/static/storage-toast.html
<https://www.postgresql.org/docs/9.5/static/storage-toast.html>
It seems to work but sometimes the tuples seem compressed
and sometime not.
I tried both with constant data and random bytes.
Thanks
Pupillo
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx <mailto:adrian.klaver@xxxxxxxxxxx>
Hi,
definition: create table stato (id bigint, dati bytea);
then I populate the dati field with 100 bytes.
https://www.postgresql.org/docs/9.5/static/storage-toast.html
"The TOAST management code is triggered only when a row value to be
stored in a table is wider than TOAST_TUPLE_THRESHOLD bytes (normally 2
kB). The TOAST code will compress and/or move field values out-of-line
until the row value is shorter than TOAST_TUPLE_TARGET bytes (also
normally 2 kB) or no more gains can be had. During an UPDATE operation,
values of unchanged fields are normally preserved as-is; so an UPDATE of
a row with out-of-line values incurs no TOAST costs if none of the
out-of-line values change."
Pupillo
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
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