For my experience, the biggest issue is that , if you have a lot of
concurrent activities, postgres opens its files through the filesystem
cache , so you have double buffering ( filesystem cache and postgresql
buffer cache ) and there is no "filesystem_options=O_DIRECT" in postgres (
there is on wal but you have issue and you can not use archive if i
remember ) and this is a quite huge drawback in terms of performance .
Other problem can be vacuum as other said. This only for a low level point
of few. If you have applications with tons of plsql and use of oracle
packages, it can not be cheap to migrate them .... ( port, modify/rewrite,
test everything ... )
Il giorno mer 11 gen 2023 alle ore 12:19 Frits Hoogland <
frits.hoogland_at_gmail.com> ha scritto:
> PostgreSQL and Oracle are two different databases.
>
> Both implement most of the SQL standards, and both contain their own
> specific implementations for all kinds of things. This is true for anything
> that directly is defined by the SQL standard, and anything beyond that.
>
> PostgreSQL contains a procedural language extension, plpgsql, that has
> similarities with Oracle's PLSQL.
>
> Out of the available general databases, I do believe PostgreSQL is most
> close to Oracle SQL and PLSQL.
>
> A few differences:
> - PostgreSQL relies on the operating system page cache for datafile
> buffering, and thus strictly employs buffered reads for these.
> - There is no equivalence of the shared pool: every backend (database
> connection) has to build its own dictionary cache, SQL cache, row cache.
> - The implementation of consistency differs between Oracle and PostgreSQL.
> Although the general way they deal with it is obvious and alike, there are
> nuanced implementation differences between the two.
>
> Oracle would perform better at huge scale with very specific configuration.
> In reality, most products using the database use it in a very basic way,
> and for these PostgreSQL can probably quite easily replace Oracle, provided
> you can change the SQL, the driver, etc.
> In fact, this is happening in a lot of places.
>
> Frits
>
>
>
> On 6 Jan 2023, at 13:36, Terrian Thomas J CTR DLA INFO OPERATIONS
> ("Tom.Terrian.ctr") <dmarc-noreply_at_freelists.org> wrote:
>
> Here are some open ended question for the group…We are starting to look at
> migrating our databases from Oracle to PostgreSQL. I know nothing about
> PostgreSQL.
>
> Has anyone done a pro’s and con’s list of Oracle vs. PostgreSQL?
> Anyone have a lesson’s learned list from migrating from Oracle to
> PostgreSQL?
> Any thoughts/comments on PostgreSQL?
> I kind of think that you get what you pay for…wouldn’t that mean that
> Oracle would outperform PostgreSQL in every way?
>
> Any comments would be appreciated.
>
> Tom
>
>
>
