Обсуждение: Normalization or Performance
Hi, Before writing this mail, I'd researched a little about this topic, and got some opinions from guys like Fabien Pascal, who argues that logical design should be separated from physical design, and other sources. As this is not fact, I'm writing to you guys, that make things work in real world. We started our first big (for our company standards) project always thinking in normalization. But once we imported legacy data into the DB, things got harder. One example is the clients status. A client might be active, inactive or pending (for many reasons). We store all the status a client have since it is in the system. To check what is the actual status of a client, we get the last status from this historical status table. This take a considerable time, so our best results were achieved building a function that checks the status and indexing this function. The problem is that indexed functions mus bu immutable, so as you can figure, if the status change after the creation of the index, the retunr of the function is still the same. What do you suggest for situations like this? Should I add a field to clients table and store its actual status, keep storing data in the historical table an control its changes with a trigger? There are other situations that are making things difficult to us. For example, one query must return the total amount a client bought in the last 90 days. It's taking too long, when we must know it for many clients, many times. So should I create summarization tables to store this kind of stuff, update it with a trigger in daily basis (for example), and solve this problem with one join? Our database is not that big. The larger table has about 7.000.000 rows. About 50.000 clients, half of them active. All that I'd point out above uses indexes for queries, etc. But even with this it's not been fast enough. We have a Dell server for this (I know, the Dell issue), a Dual Xeon 2.8, SCSI HD, 1 GB mem. Do we need better hardware for our system? -- +---------------------------------------------------+ | Alvaro Nunes Melo Atua Sistemas de Informacao | | al_nunes@atua.com.br www.atua.com.br | | UIN - 42722678 (54) 327-1044 | +---------------------------------------------------+
Alvaro Nunes Melo wrote: > Hi, > > Before writing this mail, I'd researched a little about this topic, > and got some opinions from guys like Fabien Pascal, who argues that > logical design should be separated from physical design, and other > sources. As this is not fact, I'm writing to you guys, that make > things work in real world. I believe he's right. Or at least that you should only compromise your logical design once it becomes absolutely necessary due to physical limitations. > We started our first big (for our company standards) project always > thinking in normalization. But once we imported legacy data into the > DB, things got harder. > > One example is the clients status. A client might be active, inactive > or pending (for many reasons). We store all the status a client have > since it is in the system. To check what is the actual status of a > client, we get the last status from this historical status table. > This take a considerable time, so our best results were achieved > building a function that checks the status and indexing this > function. The problem is that indexed functions mus bu immutable, so > as you can figure, if the status change after the creation of the > index, the retunr of the function is still the same. > > What do you suggest for situations like this? Should I add a field to > clients table and store its actual status, keep storing data in the > historical table an control its changes with a trigger? Trigger + history table is a common solution, it's easy to implement and there's nothing non-relational about it as a solution. > There are other situations that are making things difficult to us. > For example, one query must return the total amount a client bought > in the last 90 days. It's taking too long, when we must know it for > many clients, many times. So should I create summarization tables to > store this kind of stuff, update it with a trigger in daily basis > (for example), and solve this problem with one join? One solution I use for this sort of thing is a summary table grouped by date, and accurate until the start of today. Then, I check the summary table and the "live" table for todays information and sum those. > Our database is not that big. The larger table has about 7.000.000 > rows. About 50.000 clients, half of them active. All that I'd point > out above uses indexes for queries, etc. But even with this it's not > been fast enough. We have a Dell server for this (I know, the Dell > issue), a Dual Xeon 2.8, SCSI HD, 1 GB mem. Do we need better > hardware for our system? Swap one of your processors for more RAM and disks, perhaps. -- Richard Huxton Archonet Ltd
On Thu, Dec 02, 2004 at 03:05:55PM -0200, Alvaro Nunes Melo wrote: > Hi, > > Before writing this mail, I'd researched a little about this topic, and > got some opinions from guys like Fabien Pascal, who argues that logical > design should be separated from physical design, and other sources. As > this is not fact, I'm writing to you guys, that make things work in real > world. > > We started our first big (for our company standards) project always > thinking in normalization. But once we imported legacy data into the DB, > things got harder. > > One example is the clients status. A client might be active, inactive or > pending (for many reasons). We store all the status a client have since > it is in the system. To check what is the actual status of a client, we > get the last status from this historical status table. This take a > considerable time, so our best results were achieved building a > function that checks the status and indexing this function. The problem > is that indexed functions mus bu immutable, so as you can figure, if the > status change after the creation of the index, the retunr of the > function is still the same. > > What do you suggest for situations like this? Should I add a field to > clients table and store its actual status, keep storing data in the > historical table an control its changes with a trigger? It seems you shouldn't have to resort to this. SELECT status FROM client_status WHERE client_id = blah ORDER BY status_date DESC LIMIT 1 should be pretty fast given an index on client_id, status_date (which should be able to be unique). > There are other situations that are making things difficult to us. For > example, one query must return the total amount a client bought in the > last 90 days. It's taking too long, when we must know it for many > clients, many times. So should I create summarization tables to store > this kind of stuff, update it with a trigger in daily basis (for > example), and solve this problem with one join? This sounds like a more likely candidate for a summary table, though you might not want to use a trigger. Unless you need absolutely up-to-date information it seems like a nightly process to update the totals would be better and more efficient. > Our database is not that big. The larger table has about 7.000.000 rows. > About 50.000 clients, half of them active. All that I'd point out above > uses indexes for queries, etc. But even with this it's not been fast > enough. We have a Dell server for this (I know, the Dell issue), a Dual > Xeon 2.8, SCSI HD, 1 GB mem. Do we need better hardware for our system? Is all this on a single HD? That's going to be a huge bottleneck. You'll be much better off with a mirrored partition for your WAL files and either raid5 or raid10 for the database itself. You'd probably be better off with more memory as well. If you're going to buy a new box instead of upgrade your existing one, I'd recommend going with an Opteron because of it's much better memory bandwidth. For reference, stats.distributed.net is a dual Opteron 244 1.8GHz with 4G ram, a 200G mirror for WAL and the system files and a 6x200G RAID10 for the database (all SATA drives). The largest table 120M rows and 825,000 8k pages. I can scan 1/5th of that table via an index scan in about a minute. (The schema can be found at http://minilink.org/cvs.distributed.net/l3.sql. -- Jim C. Nasby, Database Consultant decibel@decibel.org Give your computer some brain candy! www.distributed.net Team #1828 Windows: "Where do you want to go today?" Linux: "Where do you want to go tomorrow?" FreeBSD: "Are you guys coming, or what?"
Hi, without knowing much about your system, it seems to me that the current status of a client should be represented by a status code on the client record. History is the list of *past* status codes. The full history, including the current status of a client would be obtained using a union. I had a situation which might have some parallels with yours. nthis case the tables represented orders and receivals. The status of an order item was held on a code in the receival itemss table (an order item can be received many times). This is seems to me to be not normalized as the status was actually the status of the order item, not the receival. The receival just caused the status of the order item to change. This arrangement required ridiculously complex sql and resulted in poor performance. Moving the status code to the order item and implementing a simple trigger on the receival items table cleaned things up significantly. To put it simply, if the current status of an order item is a simple attribute of the order item, then it should be in the order item table. The same might be said for your client. This is just my personal opinion though and I'm always open to alternative opinions, as I think you are. regards Iain ----- Original Message ----- From: "Alvaro Nunes Melo" <al_nunes@atua.com.br> To: "Pgsql-Performance" <pgsql-performance@postgresql.org> Sent: Friday, December 03, 2004 2:05 AM Subject: [PERFORM] Normalization or Performance > Hi, > > Before writing this mail, I'd researched a little about this topic, and > got some opinions from guys like Fabien Pascal, who argues that logical > design should be separated from physical design, and other sources. As > this is not fact, I'm writing to you guys, that make things work in real > world. > > We started our first big (for our company standards) project always > thinking in normalization. But once we imported legacy data into the DB, > things got harder. > > One example is the clients status. A client might be active, inactive or > pending (for many reasons). We store all the status a client have since > it is in the system. To check what is the actual status of a client, we > get the last status from this historical status table. This take a > considerable time, so our best results were achieved building a > function that checks the status and indexing this function. The problem > is that indexed functions mus bu immutable, so as you can figure, if the > status change after the creation of the index, the retunr of the > function is still the same. > > What do you suggest for situations like this? Should I add a field to > clients table and store its actual status, keep storing data in the > historical table an control its changes with a trigger? > > There are other situations that are making things difficult to us. For > example, one query must return the total amount a client bought in the > last 90 days. It's taking too long, when we must know it for many > clients, many times. So should I create summarization tables to store > this kind of stuff, update it with a trigger in daily basis (for > example), and solve this problem with one join? > > Our database is not that big. The larger table has about 7.000.000 rows. > About 50.000 clients, half of them active. All that I'd point out above > uses indexes for queries, etc. But even with this it's not been fast > enough. We have a Dell server for this (I know, the Dell issue), a Dual > Xeon 2.8, SCSI HD, 1 GB mem. Do we need better hardware for our system? > > -- > +---------------------------------------------------+ > | Alvaro Nunes Melo Atua Sistemas de Informacao | > | al_nunes@atua.com.br www.atua.com.br | > | UIN - 42722678 (54) 327-1044 | > +---------------------------------------------------+ > > > ---------------------------(end of broadcast)--------------------------- > TIP 8: explain analyze is your friend