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Re: Postgres as In-Memory Database?

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Em 17/11/2013 20:46, Andreas Brandl escreveu:
Edson,

Em 17/11/2013 19:26, Stefan Keller escreveu:
Hi Edson

As Rob wrote: Having a feature like an in-memory table like SQLite
has
[1] would make application cahces obsoleteand interesting to
discuss
(but that was'nt exactly what I asked above).
Hi, Stephan,

I don't think any feature you add to database server would bring
obsolescence to app server caches: app server caches have just no lag
at
all:

1) Don't need network connection to database server
2) Don't need to materialize results (for instance, I have in mind a
Java or .Net app server running hundred thousands of objects in
memory).

IMHO, no matter how much you improve database, app server caches
provides additional level of speed that cannot be achieved by
database.

That said, I still can see huge improvements in database server.
Having strong in memory operation would bring substantial
improvements.
For instance, if you have in-memory database (tables, indexes, etc)
for
all sort of queries, and just **commit** to disks, then you will have
unprecedent performance.
I would get benefit from this architecture, since typical customer
database has < 64Gb on size (after 2 or 3 years of data recording).
So,
a database server with 64Gb of memory would keep everything in
memory,
and just commit data to disc.

In this case, commited data would be instantly available to queries
(because they are all in memory) while log (changes) is recorded in a
fast disk (a SSD, perhaps) and then those changes are made persistent
data, written async into slow massive disks (SCSI or SAS).

This would allow also a hybrid operation (too keep as much data pages
as
possible in memory, with a target of 50% or more in memory).

When database server is started, it would have lazy load (data is
loaded
and kept in memory as it is used) or eager load (for slower startup
but
faster execution).
not sure I fully understand your point. Isn't this the typical mode-of-operation plus added cache warming?

Anyways, just wanted to point you to [1] which gives a good overview of cache warming techniques.

Regards,
Andreas

[1] http://raghavt.blogspot.fr/2012/04/caching-in-postgresql.html


Worndeful, never knew about it.
I'm ready ASAP.

Regards

Edson


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