Re: Array, bytea and large objects
| От | Filip Rembiałkowski |
|---|---|
| Тема | Re: Array, bytea and large objects |
| Дата | |
| Msg-id | 92869e660902050718p4e6f8c9au1664cf6f6c953435@mail.gmail.com обсуждение исходный текст |
| Ответ на | Array, bytea and large objects (David Wall <d.wall@computer.org>) |
| Ответы |
Re: Array, bytea and large objects
(David Wall <d.wall@computer.org>)
|
| Список | pgsql-general |
2009/2/4 David Wall <d.wall@computer.org>
yes.
http://jdbc.postgresql.org/documentation/83/index.html
see Large Objects and "Storing Binary Data"
transparent encryption is not implemented in the driver but of course it is possible.
yes you could, but what for?
what's wrong with many rows? create table kvstore(key text primary key,value text);
what stops you from using single SELECT to get all these kv pairs?
as many as the max number of different OIDs .. minus the number of system objects
so I think 2^31 large objects is possible without problem.
that's how it is actually implemented - you probably know it already :)
yes - and the TOAST tables if it's larger than 1/3 of a page or so. search for TOAST details if you're interested.
I guess ARRAYs are serialized and stored according to same rules as any other data (TOAST mechanism).
most of your questions are answered in the documentation and FAQ.
I'd avoid LO unless you really need streaming (block-wise) access.
First, LOs seem to allow an OID column to be added to any number of tables, but is it true that the actual large object data is stored in a single table (pg_largeobject?).
yes.
If so, wouldn't this become a bottleneck if LOs were used frequently? Even vacuuming and vacuumlo must create a lot of pressure on that one table if LOs are used extensively. And can you backup a table with an OID column and get only those LOs referenced in the dump?
Does the JDBC library support LO streaming? Can I receive data, compress, encrypt and stream into the database as well as do the opposite when reading it back?
http://jdbc.postgresql.org/documentation/83/index.html
see Large Objects and "Storing Binary Data"
transparent encryption is not implemented in the driver but of course it is possible.
If I have an "unlimited" number of name-value pairs that I'd like to get easy access to for flexible reports, could I store these in two arrays (one for name, the other for value) in a table so that if I had 10 name-value pairs or 200 name-value pairs, I could store these into a single row using arrays so I could retrieve all name-value pairs in a single SELECT from the db?
yes you could, but what for?
what's wrong with many rows? create table kvstore(key text primary key,value text);
what stops you from using single SELECT to get all these kv pairs?
How are these arrays stored -- does it use an underlying type like LO or BYTEA?
How big can an LO get? Is it 2GB?
no, much larger. I guess it's limited by max table size.
see http://www.postgresql.org/docs/faqs.FAQ.html#item4.4
see http://www.postgresql.org/docs/faqs.FAQ.html#item4.4
How many LO fields can I have in a database?
as many as the max number of different OIDs .. minus the number of system objects
so I think 2^31 large objects is possible without problem.
It seems that the LO may even be implemented as an OID with one or more BYTEA storage structure in the pg_largeobject table (loid,pageno,data). Is that true?
that's how it is actually implemented - you probably know it already :)
How big is a "page"? Maybe an LO is more efficient than a BYTEA if it's bigger than one page?
default and recommended page size is 8 kB.
How big can a BYTEA get? Is it 1GB?
Yes.
At what size does it make more sense to store in LO instead of a BYTEA (because of all the escaping and such)?
How many BYTEA fields can I have in a database?
no limit (other than limits mentioned in the FAQ)
Are the BYTEA fields stored in the same table as the rest of the data?
yes - and the TOAST tables if it's larger than 1/3 of a page or so. search for TOAST details if you're interested.
I believe this is yes, so a backup of that table will include the binary data, too, correct?
yes
How big can an ARRAY get? Is it 1GB?
yes
How many ARRAY fields can I have in a table or database? Are there limits?
same as bytea or any other type
Are the ARRAY fields stored in the same table as the rest of the data?
I guess ARRAYs are serialized and stored according to same rules as any other data (TOAST mechanism).
Sorry for all the questions, but I'm trying to research it but the info is not always clear (and perhaps some of the stuff I find is not even true).
most of your questions are answered in the documentation and FAQ.
I am wondering if when my encrypted XML data is small, should I choose to store it in a table using BYTEA so that each "record" in my application (which uses the encrypted XML name-value storage) is not forced to be in a single pg_largeobject table, and use LO when my data reaches a threshold size? Thoughts?
I'd avoid LO unless you really need streaming (block-wise) access.
cheers,
--
Filip Rembiałkowski
JID,mailto:filip.rembialkowski@gmail.com
http://filip.rembialkowski.net/
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