Thread: re : PHP and persistent connections
Set the number of connection in php.ini to 2 Exemple : [PostgresSQL] pgsql.allow_persistent = On ; allow or prevent persistent link pgsql.max_persistent = 2 ; maximum number of persistent links. -1 means no limit pgsql.max_links = 2 ; maximum number of links (persi stent+non persistent). -1 means no limit Because if you keep the default value each apache process has an ulimited number of connection. So if your httpd start with 10 child process you have 20 persistent connections. So be carefull about the number of apache process and check the value of persistent connection in php.ini in order to adjust it. Cheers PEJAC Pascal
On Thu, Nov 23, 2000 at 04:53:35PM +0100, some SMTP stream spewed forth: > Set the number of connection in php.ini to 2 I tried doing this, with the max set to 1, 2, and 3; but the number of backends continues to grow until smacking into the ceiling. What is controlled by max_persistent? It seems like PHP is just ignoring this value. I apologize for bringing PHP onto this list, but it is relevant. Should not the backends die at *some* point? Using regular connections almost triples the script's execution time. (It is still under .5 seconds, but...) It seems like the number of Apache processes would have to be *really* low or the number of backends would have to be *really* high. Our backend limit is still the default 32. I thank you. gh > > Exemple : > [PostgresSQL] > pgsql.allow_persistent = On ; allow or prevent persistent link > pgsql.max_persistent = 2 ; maximum number of persistent links. -1 > means no limit > pgsql.max_links = 2 ; maximum number of links (persi > stent+non persistent). -1 means no limit > > Because if you keep the default value each apache process > has an ulimited number of connection. So if your > httpd start with 10 child process you have 20 persistent connections. So be carefull about the number of apache > process and check the value of persistent connection > in php.ini in order to adjust it. > > Cheers > > PEJAC Pascal > >
On Thu, Nov 23, 2000 at 10:14:17AM -0600, some SMTP stream spewed forth:
> On Thu, Nov 23, 2000 at 04:53:35PM +0100, some SMTP stream spewed forth:
> > Set the number of connection in php.ini to 2
>
> I tried doing this, with the max set to 1, 2, and 3; but the number
> of backends continues to grow until smacking into the ceiling.
> What is controlled by max_persistent? It seems like PHP is just
> ignoring this value.
Um, heh, nevermind. (*heads to corner for to bury his head in the sand*).
It turns out that the number of max_persistent is linked to the httpd
processes in some difficult-to-describe way.
e.g.
MinSpareServers 10
MaxSpareServers 20
StartServers 15
MaxClients 300 (I do not know why that is so high, but oh well.)
KeepAlive On
pgsql.max_persistent = 2
pgsql.max_links = -1 (no limit).
Now, the number of backends and httpd processes starts as
2 postgres, and 17 httpd. I guess because of the StartServers 15
The max that I can reach by fetching only the script that uses
one persistent connection is
22 postgres, and 22 or 23 httpd.
It appears to be that PHP opens a new "persistent" connection when the
persistent connection (backend?) is "occupied". I believe someone made a
comment about not doing connection pooling.
I wish there were some way to keep the extra 17 or so postgres backends
from hanging around. Maybe I am just missing something in the concept.
I do not know what will happen with PHP when there are more than one
different (i.e. different username, database) persistent connections.
I suppose they would be affected by the max_persistent. (?).
Anyway, I thank you all for your assistance.
"99% of Geeks love databases; Geeks love statistics because they
encourage the use of databases." ;-))
gh
.
Howdy, > It turns out that the number of max_persistent > is linked to the httpd processes in some > difficult-to-describe way. It's not that hard to describe. The max_persistent/max_links values are per Apache process. Thus if you have: pgsql.max_persistent = 2 and MaxClients 300 You could potentially reach a state where you are maintaining 600 persistant connections to the database (if your PHP scripts actually pg_pconnect() with two different connect strings). I think that if you are using persistant connections you may as well set MaxClients to the same number of database backends you are allowing (or possibly a bit less if you need other connections to the database). There's no real point in allowing more Maxclients as they'll just start hitting connect errors anyway. Obviously this isn't the most efficient use of backends because a fair amount of the time the Apache processes won't be using them at all (they'll be sitting there doing nothing, or serving images or other static content). If your application is big enough you may benefit from serving static content (images etc) from a different server, so the Apache processes with persistant connection to backends are being used more heavily for database work. Ie if you normally have 100 Apache processes running on your webserver and you are using one persistant connection per process you will need 100 backends. However if at any one time those 60% of those processes are serving images then you could have an Apache server on one machine serving those images and only need 40 Apache processes and therefore 40 backends on the Apache server that serves the PHP script. You'll be tuning each machine for a more specific task, rather than having one machine doing all sorts of different stuff. > I do not know what will happen with PHP when there are more than one > different (i.e. different username, database) persistent connections. > I suppose they would be affected by the max_persistent. (?). If you want persistant connections to two different database/username pairs then you need to have max_persistant=2, one for each different connection string. If you have one database that is used a lot and one that isn't, you may wish to set max_persistant to 1 and max_clients to 2. Use pg_pconnect() for the one accessed a lot and pg_connect() for the other. Set Apache MaxClients to X and the max number of PG backends to X + Y, where Y allows for the load required by the short lived pg_connect()s. As you've probably noticed, balancing all this is a rather manual process. Perhaps Apache 2.0 will make way for some connection pooling. I hope that wasn't too confusing. Oh, and if you are using pg_close() I don't think it works in any currently released PHP4 versions. See: http://bugs.php.net/bugs.php?id=7007 From the changelog: http://cvs.php.net/viewcvs.cgi/~checkout~/php4/ChangeLog?rev=1.541&conte nt-type=text/plain it seems a fix went in to CVS on 2000-11-03. -- Paul McGarry mailto:paulm@opentec.com.au Systems Integrator http://www.opentec.com.au Opentec Pty Ltd http://www.iebusiness.com.au 6 Lyon Park Road Phone: (02) 9878 1744 North Ryde NSW 2113 Fax: (02) 9878 1755755
On Fri, Nov 24, 2000 at 03:17:59PM +1100, some SMTP stream spewed forth: > Howdy, > > > It turns out that the number of max_persistent > > is linked to the httpd processes in some > > difficult-to-describe way. > > It's not that hard to describe. The max_persistent/max_links values are > per Apache process. It was difficult to describe because I was not recieving consistent results in experiments due to a number of factors. It makes sense now. > > Thus if you have: > > pgsql.max_persistent = 2 > > and > > MaxClients 300 > > You could potentially reach a state where you are maintaining 600 > persistant connections to the database (if your PHP scripts actually > pg_pconnect() with two different connect strings). > > I think that if you are using persistant connections you may as well set > MaxClients to the same number of database backends you are allowing (or > possibly a bit less if you need other connections to the database). > There's no real point in allowing more Maxclients as they'll just start > hitting connect errors anyway. Well, see, the thing is, we do webhosting for a number of different domains from the same server so the number of MaxClients needs to be high. I think that 300 is obscene, as the server is not powerful enough to handle 300 apache processes without dumping a large number of them into swap space, not to mention the processing, but no matter what, we would have several extra postgres backends just hanging around wasting ram. Only a few unique persistent connections would be in use at any given time as only a few domains use the database. This has made me realize just how completely braindead our server setup is. ;-) It seems that we would to bring up a seperate database server, very soon. > > Obviously this isn't the most efficient use of backends because a fair > amount of the time the Apache processes won't be using them at all > (they'll be sitting there doing nothing, or serving images or other > static content). Just what I was thinking. Connection pooling would avoid that, correct? > > If your application is big enough you may benefit from serving static > content (images etc) from a different server, so the Apache processes > with persistant connection to backends are being used more heavily for > database work. True, but in this case probably moving the database to a different server would make more sense because most of the backends would be serving content that is completely unrelated to the database. > > Ie if you normally have 100 Apache processes running on your webserver > and you are using one persistant connection per process you will need > 100 backends. However if at any one time those 60% > of those processes are serving images then you could have an Apache > server on one machine serving those images and only need 40 Apache > processes and therefore 40 backends on the Apache server that serves the > PHP script. You'll be tuning each machine for a more specific task, > rather than having one machine doing all sorts of different stuff. > > > I do not know what will happen with PHP when there are more than one > > different (i.e. different username, database) persistent connections. > > I suppose they would be affected by the max_persistent. (?). > > If you want persistant connections to two different database/username > pairs then you need to have max_persistant=2, one for each different > connection string. > > If you have one database that is used a lot and one that isn't, you may > wish to set max_persistant to 1 and max_clients to 2. Use pg_pconnect() > for the one accessed a lot and pg_connect() for the other. Set Apache > MaxClients to X and the max number of PG backends to X + Y, where Y > allows for the load required by the short lived pg_connect()s. > > As you've probably noticed, balancing all this is a rather manual > process. > Perhaps Apache 2.0 will make way for some connection pooling. > > I hope that wasn't too confusing. Your explanation makes perfect sense. A Zen sort of understanding has come to me through experimenting with different settings. How would persistent connections fit into a dual-server setup where one server is handling all of the webserving and the other simply handles the database data-serving? The number of backends on the database server would be independent of the number of Apache processes on the webserver inasmuch as there could be 75 Apache processes but only 25 are connected to backends on the database server, correct? There would not necessarily be any Apache stuff on the database server? > > Oh, and if you are using pg_close() I don't think it works > in any currently released PHP4 versions. See: This seems to be true. I ran into some fun link errors while connecting and disconnecting more than once in a script. Thanks again, and again. gh > http://bugs.php.net/bugs.php?id=7007 > >From the changelog: > http://cvs.php.net/viewcvs.cgi/~checkout~/php4/ChangeLog?rev=1.541&conte > nt-type=text/plain > it seems a fix went in to CVS on 2000-11-03. > > > -- > Paul McGarry mailto:paulm@opentec.com.au > Systems Integrator http://www.opentec.com.au > Opentec Pty Ltd http://www.iebusiness.com.au > 6 Lyon Park Road Phone: (02) 9878 1744 > North Ryde NSW 2113 Fax: (02) 9878 1755755
At 12:47 PM 11/24/00, GH wrote: >On Fri, Nov 24, 2000 at 03:17:59PM +1100, some SMTP stream spewed forth: > > Oh, and if you are using pg_close() I don't think it works > > in any currently released PHP4 versions. See: > >This seems to be true. I ran into some fun link errors while >connecting and disconnecting more than once in a script. This sounds disturbing! How then should I go about closing persistent connections? Can I close them at all? Would pg_close() work if I used it on non-persistent connections? Thanks in advance, Mikah
GH wrote: > On Fri, Nov 24, 2000 at 03:17:59PM +1100, some SMTP stream spewed forth: > > Howdy, > > > It turns out that the number of max_persistent > > > is linked to the httpd processes in some > > > difficult-to-describe way. > > It's not that hard to describe. The max_persistent/max_links values are > > per Apache process. > It was difficult to describe because I was not recieving consistent > results in experiments due to a number of factors. It makes sense now. I've copied this email exchange over to my PHP folder.. I see what I can do do to improve the online documentation. :-) > Well, see, the thing is, we do webhosting for a number of different > domains from the same server so the number of MaxClients needs to be > high. I think that 300 is obscene, as the server is not powerful enough > to handle 300 apache processes without dumping a large number of them > into swap space, not to mention the processing, but no matter what, we > would have several extra postgres backends just hanging around wasting > ram. > Only a few unique persistent connections would be in use at any given > time as only a few domains use the database. Give them their own apache? You can set up two apache instances on one box, set up one with lots of backends, set up the other to match the applicable db usage... You could make a postgres+apache box for these few clients... > This has made me realize just how completely braindead our server setup > is. ;-) It seems that we would to bring up a seperate database > server, very soon. Depends on the load. I'm serving 429 domains off of PHP/PostgreSQL, using non-persistant connections (even though almost every page has a select or two), and it's working just fine. My biggest selects only return a few hundred rows, my small inserts/updates are done in PHP, the big ones (4,000+ rows) are just parsed into files that a Perl/cron job takes care of them. It also depends, obviously, on how you write your code for all of this, how good the hardware is, etc. (PII/500, 512Mb of RAM, RH 6.2 for the above) > > Obviously this isn't the most efficient use of backends because a fair > > amount of the time the Apache processes won't be using them at all > > (they'll be sitting there doing nothing, or serving images or other > > static content). > Just what I was thinking. Connection pooling would avoid that, correct? > > If your application is big enough you may benefit from serving static > > content (images etc) from a different server, so the Apache processes > > with persistant connection to backends are being used more heavily for > > database work. > True, but in this case probably moving the database to a different server > would make more sense because most of the backends would be serving > content that is completely unrelated to the database. Well, here's the problem: 1 apache/php/postgres thread = 1 possible persistant postgres connection if you run up 200 threads on _any_ server instance, that means you need 200 waiting backends, if that server is also doing postgres content with persistant connections anywhere in that server. I think the idea being referred to works like this: In a big, mega-hit app, you put your simple content on a simple server, so the web pages reference GIF's/frames/whatever stored there, rather than on a heavy-use box. This means that the clients go to *another* web server for that non-dynamic content. > How would persistent connections fit into a dual-server setup where one > server is handling all of the webserving and the other simply handles the > database data-serving? Er... well, if you db load was really heavy, this would make sense, but your problem is about having all of the webserving in one place. > The number of backends on the database server would be independent > of the number of Apache processes on the webserver inasmuch as there > could be 75 Apache processes but only 25 are connected to backends on the > database server, correct? All 75 Apache processes might eventually try to serve up the db pages. So all 75 *could* eventually want persistant connections. You can't control which process gets which page. > There would not necessarily be any Apache stuff on the database server? Not if you don't want it, no. Keep in mind that using _non_ persistant connections on this setup will be even slower, as well. -Ron -- Brought to you from iBop the iMac, a MacOS, Win95, Win98, LinuxPPC machine, which is currently in MacOS land. Your bopping may vary.
On Fri, Nov 24, 2000 at 02:48:18PM +0800, some SMTP stream spewed forth: > > At 12:47 PM 11/24/00, GH wrote: > >On Fri, Nov 24, 2000 at 03:17:59PM +1100, some SMTP stream spewed forth: > > > Oh, and if you are using pg_close() I don't think it works > > > in any currently released PHP4 versions. See: > > > >This seems to be true. I ran into some fun link errors while > >connecting and disconnecting more than once in a script. > > This sounds disturbing! Maybe it should, I thought it was. Who knows. > > How then should I go about closing persistent connections? Can I close > them at all? You cannot, by design and purpose, close persistent connections. You could kill the postgres backend, but that is not quite the same. ;-) > Would pg_close() work if I used it on non-persistent connections? My experience has caused me to believe that no, it will not. That is not final, as I do not have true proof. > > Thanks in advance, No prob, we are here to benefit each other. It seems like PHP would open other new connections using pg_connect(), but would not close them. Has anyone had experiences other than this? gh > > Mikah >
On Fri, Nov 24, 2000 at 12:52:34AM -0700, some SMTP stream spewed forth: > GH wrote: > > On Fri, Nov 24, 2000 at 03:17:59PM +1100, some SMTP stream spewed forth: > > > Howdy, > > > > It turns out that the number of max_persistent > > > > is linked to the httpd processes in some > > > > difficult-to-describe way. > > > It's not that hard to describe. The max_persistent/max_links values are > > > per Apache process. > > It was difficult to describe because I was not recieving consistent > > results in experiments due to a number of factors. It makes sense now. > > I've copied this email exchange over to my PHP folder.. I see what I can do > do to improve the online documentation. :-) Great. Thanks. > > > Well, see, the thing is, we do webhosting for a number of different > > domains from the same server so the number of MaxClients needs to be > > high. I think that 300 is obscene, as the server is not powerful enough > > to handle 300 apache processes without dumping a large number of them > > into swap space, not to mention the processing, but no matter what, we > > would have several extra postgres backends just hanging around wasting > > ram. > > Only a few unique persistent connections would be in use at any given > > time as only a few domains use the database. > > Give them their own apache? You can set up two apache instances on one box, > set up one with lots of backends, set up the other to match the applicable > db usage... > You could make a postgres+apache box for these few clients... Er, I think I missed something. You mean give them their own Apache instance using a seperate ip? Is it /possible/ to have a group of httpd processes (Apache) share a group of Postgres backends without having one backend to one httpd? That would be connection pooling, correct? Which is not yet possible? > > > This has made me realize just how completely braindead our server setup > > is. ;-) It seems that we would to bring up a seperate database > > server, very soon. > > Depends on the load. I'm serving 429 domains off of PHP/PostgreSQL, > using non-persistant connections (even though almost every page has > a select or two), and it's working just fine. My biggest selects only > return a few hundred rows, my small inserts/updates are done in PHP, > the big ones (4,000+ rows) are just parsed into files that a Perl/cron job > takes care of them. It also depends, obviously, on how you write your > code for all of this, how good the hardware is, etc. > (PII/500, 512Mb of RAM, RH 6.2 for the above) That makes sense. The only reason I am so zealous about persistent connections is that I have seen them be 3 times as fast as regular connections. > > > > Obviously this isn't the most efficient use of backends because a fair > > > amount of the time the Apache processes won't be using them at all My main question now is, how can I avoid this? I would have to go to non-persistent connections, correct? I think I further understand things now. So, persistent connections create a one-to-one ratio of db-using Apache processes and Postgres backends, no matter what? The only way to avoid such a one-to-one setup would be to use non-persistent connections or do connection pooling? So, even if the database were running on a seperate server, each apache procees on the main server would require one backend process on the db server? > > -Ron > > -- > Brought to you from iBop the iMac, a MacOS, Win95, Win98, LinuxPPC machine, > which is currently in MacOS land. Your bopping may vary.
I have a couple of other questions that I believe are not ansvered in
the docs anywhere.
Do the "persistent-connected" Postgres backends ever timeout or die?
Is it possible to set something like a timeout for persistent connctions?
(Er, would that be something that someone would want
to do? A Bad Thing?)
What happens when the httpd process that held a persistent connection
dies? Does "its" postgres process drop the connection and wait for
others? When the spare apache processes die, the postgres processes
remain.
Thanks.
gh
We're in quote hell. Yay. GH wrote: > > On Fri, Nov 24, 2000 at 12:52:34AM -0700, some SMTP stream spewed forth: > > GH wrote: > > > On Fri, Nov 24, 2000 at 03:17:59PM +1100, some SMTP stream spewed forth: > > > > Howdy, > > Give them their own apache? You can set up two apache instances on one box, > > set up one with lots of backends, set up the other to match the applicable > > db usage... > > You could make a postgres+apache box for these few clients... > Er, I think I missed something. > You mean give them their own Apache instance using a seperate ip? Yes. Apache one, httpd, serves 14 domains, conf files in /usr/local/apache/conf. pgsql.max_persistent = 1 MaxClients 8 Apache two, httpd2, serves 327 domains, conf files in /usr/local/apache2/conf. Max clients 150 (no postgres backends, no PHP) > Is it /possible/ to have a group of httpd processes (Apache) share a > group of Postgres backends without having one backend to one httpd? > That would be connection pooling, correct? Which is not yet possible? Apache's process management, AFAIK, makes this fairly difficult. As in: "I've never seen it, and I can't find docs on on, maybe v.2 will have better support for children sharing common resources". > > Depends on the load. I'm serving 429 domains off of PHP/PostgreSQL, > > using non-persistant connections (even though almost every page has > > a select or two), and it's working just fine. My biggest selects only > > return a few hundred rows, my small inserts/updates are done in PHP, > > the big ones (4,000+ rows) are just parsed into files that a Perl/cron job > > takes care of them. It also depends, obviously, on how you write your > > code for all of this, how good the hardware is, etc. > > (PII/500, 512Mb of RAM, RH 6.2 for the above) > That makes sense. The only reason I am so zealous about persistent > connections is that I have seen them be 3 times as fast as regular > connections. Hm. I havn't. In PHP, one connection for the duration of a single page (pg_connect()) takes as much time as a new persistant connection (pg_pconnect()). Since you're often only creating one connection per page, and running a single transaction on it, the main difference would be in your connection setup... how did you test this? (I'm just curious). Is it a usage test (real, live, use) or a bench test (push to a limit that won't be reached in actual use.) I have one horribly written app, that does maybe 50 _different_ selects on one page, and it's still under two seconds per user.... > > > > Obviously this isn't the most efficient use of backends because a fair > > > > amount of the time the Apache processes won't be using them at all > My main question now is, how can I avoid this? Serve the postgres pages from a different server instance, on the same machine, or a different one. > I would have to go to non-persistent connections, correct? You could use persistant connections on a different server/instance, or use non-persistant and loose ~10ms per page, less time than your average 10K GIF takes up on a 56K download. You see, persistant PHP connections offer *no other value*, at all. None. (it's a common error for new PHP folks to think that a web server will somehow track their connections.) All it does is reduce setup time on a page. No "session", no "tracking", nada. It reduces your connection time for the page, but not significanly enough for users to know, or care (IME). In web-page uses, the time is pretty much irrelevant, because you only need one or two connections per page to get most of your data out. Persistant connections are an interesting idea, but they don't offer much. See: http://www.php.net/manual/features.persistent-connections.php > So, persistent connections create a one-to-one ratio of > db-using Apache processes and Postgres backends, no matter what? Almost. You can have more persistant connections for each apache child, but each child may look for one. So it may be 5 apache to 5 postgres, or 5 apache to 50 postgres, if needed (of course, if you had that many conections, you may want to re-architect anyways) > The only way to avoid such a one-to-one setup would be to > use non-persistent connections or do connection pooling? I'm still not following you on the "pooling". Apache doesn't, AFAICT, offer this in each child. Each child is its own application, it's own apache+php+postgres. Postgres doesn't care. PHP doesn't care. Apache cares. If you give each child piece 5 postgres connections, and have 10 children, you need up to 50 backends. > So, even if the database were running on a seperate server, > each apache procees on the main server would require one backend process > on the db server? Yup. If it was going to pull a postgres+PHP page, it would. You see, apache doesn't work in a space where one apache process can crash the whole thing. Each piece is isolated. This means that each piece needs it's own resources. Compare this to other engines, where a single crash on one serving instance takes down the _entire_ server, and it makes sense (if the pool is down, it all goes down, a la IIS). "It scales, but not that way". :-( -Ronabop -- Brought to you from iBop the iMac, a MacOS, Win95, Win98, LinuxPPC machine, which is currently in MacOS land. Your bopping may vary.
On Fri, Nov 24, 2000 at 04:52:27AM -0700, some SMTP stream spewed forth: > We're in quote hell. > Yay. Ah, but now the hell thickens. ;-) > > GH wrote: > > > > On Fri, Nov 24, 2000 at 12:52:34AM -0700, some SMTP stream spewed forth: > > > GH wrote: > > > > On Fri, Nov 24, 2000 at 03:17:59PM +1100, some SMTP stream spewed forth: > > > > > Howdy, > > > Give them their own apache? You can set up two apache instances on one box, > > > set up one with lots of backends, set up the other to match the applicable > > > db usage... > > > You could make a postgres+apache box for these few clients... > > Er, I think I missed something. > > You mean give them their own Apache instance using a seperate ip? > > Yes. > > Apache one, httpd, serves 14 domains, conf files in /usr/local/apache/conf. > pgsql.max_persistent = 1 > MaxClients 8 > > Apache two, httpd2, serves 327 domains, conf files in /usr/local/apache2/conf. > Max clients 150 (no postgres backends, no PHP) I see. > > > Is it /possible/ to have a group of httpd processes (Apache) share a > > group of Postgres backends without having one backend to one httpd? > > That would be connection pooling, correct? Which is not yet possible? > > Apache's process management, AFAIK, makes this fairly difficult. As in: > "I've never seen it, and I can't find docs on on, maybe v.2 will > have better support for children sharing common resources". > Just checking. I had heard (and expected) that it did not -- for the same reason. > > > Depends on the load. I'm serving 429 domains off of PHP/PostgreSQL, > > > using non-persistant connections (even though almost every page has > > > a select or two), and it's working just fine. My biggest selects only > > > return a few hundred rows, my small inserts/updates are done in PHP, > > > the big ones (4,000+ rows) are just parsed into files that a Perl/cron job > > > takes care of them. It also depends, obviously, on how you write your > > > code for all of this, how good the hardware is, etc. > > > (PII/500, 512Mb of RAM, RH 6.2 for the above) > > That makes sense. The only reason I am so zealous about persistent > > connections is that I have seen them be 3 times as fast as regular > > connections. > > Hm. > > I havn't. In PHP, one connection for the duration of a single > page (pg_connect()) takes as much time as a new persistant connection > (pg_pconnect()). Since you're often only creating one connection per page, > and running a single transaction on it, the main difference > would be in your connection setup... how did you test this? (I'm just > curious). Is it a usage test (real, live, use) or a bench test (push > to a limit that won't be reached in actual use.) I have one horribly > written app, that does maybe 50 _different_ selects on one page, > and it's still under two seconds per user.... "Test" is a strong word. ;-) I have a timer set on a page. The overall exec time is less that 1-tenth of a second using persistent connections, so long as a connection exists. Using regular connections, the exec time soars (;-)) to a whopping 3-tenths or so. So, no big fat deal. The exec time is low enough that the effects of the connections shine, but in general are insignificant. If the script in discussion did anything worthwhile, I doubt that I would notice anything even close to 3x. > > > > > > Obviously this isn't the most efficient use of backends because a fair > > > > > amount of the time the Apache processes won't be using them at all > > My main question now is, how can I avoid this? > > Serve the postgres pages from a different server instance, on the same > machine, or a different one. > > > I would have to go to non-persistent connections, correct? > > You could use persistant connections on a different server/instance, > or use non-persistant and loose ~10ms per page, less time than your average > 10K GIF takes up on a 56K download. > > You see, persistant PHP connections offer *no other value*, at all. None. > (it's a common error for new PHP folks to think that a web server > will somehow track their connections.) All it does is reduce setup time on a > page. No "session", no "tracking", nada. It reduces your connection > time for the page, but not significanly enough for users to know, > or care (IME). In web-page uses, the time is pretty much irrelevant, > because you only need one or two connections per page to get most > of your data out. Persistant connections are an interesting idea, > but they don't offer much. See: > http://www.php.net/manual/features.persistent-connections.php I have read it (note: the phrasing seems to be a bit "messy"), but for some reason I must have missed what it was saying. I "get it" now. > > > So, persistent connections create a one-to-one ratio of > > db-using Apache processes and Postgres backends, no matter what? > > Almost. You can have more persistant connections for each apache > child, but each child may look for one. So it may be 5 apache > to 5 postgres, or 5 apache to 50 postgres, if needed (of course, > if you had that many conections, you may want to re-architect anyways) > > > The only way to avoid such a one-to-one setup would be to > > use non-persistent connections or do connection pooling? > > I'm still not following you on the "pooling". Apache doesn't, AFAICT, I almost knew that it did not. But I was trying to re-affirm my grasp of just what "pooling" would do. > offer this in each child. Each child is its own application, it's own > apache+php+postgres. Postgres doesn't care. PHP doesn't care. Apache > cares. If you give each child piece 5 postgres connections, and have > 10 children, you need up to 50 backends. > > > So, even if the database were running on a seperate server, > > each apache procees on the main server would require one backend process > > on the db server? > > Yup. If it was going to pull a postgres+PHP page, it would. You see, > apache doesn't work in a space where one apache process can crash the > whole thing. Each piece is isolated. This means that each piece needs > it's own resources. Compare this to other engines, where a single > crash on one serving instance takes down the _entire_ server, and > it makes sense (if the pool is down, it all goes down, a la IIS). > > "It scales, but not that way". :-( Got it. Maybe this thread will finally pass away now. ;-) Thanks again. gh > > -Ronabop > > -- > Brought to you from iBop the iMac, a MacOS, Win95, Win98, LinuxPPC machine, > which is currently in MacOS land. Your bopping may vary.
GH <grasshacker@over-yonder.net> writes:
> Do the "persistent-connected" Postgres backends ever timeout or die?
No. A backend will sit patiently for the client to send it another
query or close the connection.
(Barely on topic: in recent releases, the backend does set TCP
"keepalive" mode on the client socket. On a cross-machine connection,
this causes the kernel to ping every so often on an idle connection, to
make sure that the peer machine is still alive and still believes the
connection is open. However, this does not guard against a client
process that is holding connections open without any intention of using
them again soon --- it only protects against half-open connections left
over after a system crash at the client end. In any case, I believe the
total time delay before declaring the connection lost has to be an hour
or more in a spec-compliant TCP implementation.)
> Is it possible to set something like a timeout for persistent connctions?
> (Er, would that be something that someone would want
> to do? A Bad Thing?)
This has been suggested before, but I don't think any of the core
developers consider it a good idea. Having the backend arbitrarily
disconnect on an active client would be a Bad Thing for sure. Hence,
any workable timeout would have to be quite large (order of an
hour, maybe? not milliseconds anyway). And that means that it's not
an effective solution for the problem. Under load, a webserver that
wastes backend connections will run out of available backends long
before a safe timeout would start to clean up after it.
To my mind, a client app that wants to use persistent connections
has got to implement some form of connection pooling, so that it
recycles idle connections back to a "pool" for allocation to task
threads that want to make a new query. And the threads have to release
connections back to the pool as soon as they're done with a transaction.
Actively releasing an idle connection is essential, rather than
depending on a timeout.
I haven't studied PHP at all, but from this conversation I gather that
it's only halfway there...
regards, tom lane
Note: CC'd to Hackers, as this has wandered into deeper feature issues. Tom Lane wrote: > GH <grasshacker@over-yonder.net> writes: > > Do the "persistent-connected" Postgres backends ever timeout or die? > No. A backend will sit patiently for the client to send it another > query or close the connection. This does have an unfortunate denial-of-service implication, where an attack can effectively suck up all available backends, and there's no throttle, no timeout, no way of automatically dropping these.... However, the more likely possibility is similar to the problem that we see in PHP's persistant connections.... a normally benign connection is inactive, and yet it isn't dropped. If you have two of these created every day, and you only have 16 backends, after 8 days you have a lockout. On a busy web site or another busy application, you can, of course, exhaust 64 backends in a matter of minutes. > > Is it possible to set something like a timeout for persistent connctions? > > (Er, would that be something that someone would want > > to do? A Bad Thing?) > This has been suggested before, but I don't think any of the core > developers consider it a good idea. Having the backend arbitrarily > disconnect on an active client would be a Bad Thing for sure. Right.... but I don't think anybody has suggested disconnecting an *active* client, just inactive ones. > Hence, > any workable timeout would have to be quite large (order of an > hour, maybe? not milliseconds anyway). The mySQL disconnect starts at around 24 hours. It prevents a slow accumulation of unused backends, but does nothing for a rapid accumulation. It can be cranked down to a few minutes AFAIK. > And that means that it's not > an effective solution for the problem. Under load, a webserver that > wastes backend connections will run out of available backends long > before a safe timeout would start to clean up after it. Depends on how it's set up... you see, this isn't uncharted territory, other web/db solutions have already fought with this issue. Much like the number of backends set up for pgsql must be static, a timeout may wind up being the same way. The critical thing to realize is that you are timing out _inactive_ connections, not connections in general. So provided that a connection provided information about when it was last used, or usage set a counter somewhere, it could easily be checked. > To my mind, a client app that wants to use persistent connections > has got to implement some form of connection pooling, so that it > recycles idle connections back to a "pool" for allocation to task > threads that want to make a new query. And the threads have to release > connections back to the pool as soon as they're done with a transaction. > Actively releasing an idle connection is essential, rather than > depending on a timeout. > > I haven't studied PHP at all, but from this conversation I gather that > it's only halfway there... Well...... This is exactly how apache and PHP serve pages. The problem is that apache children aren't threads, they are separate copies of the application itself. So a single apache thread will re-use the same connection, over and over again, and give that conection over to other connections on that apache thread.. so in your above model, it's not really one client application in the first place. It's a dynamic number of client applications, between one and hundreds or so. So to turn the feature request the other way 'round: "I have all sorts of client apps, connecting in different ways, to my server. Some of the clients are leaving their connections open, but unused. How can I prevent running out of backends, and boot the inactive users off?" -Ronabop -- Brought to you from iBop the iMac, a MacOS, Win95, Win98, LinuxPPC machine, which is currently in MacOS land. Your bopping may vary.
At 05:26 PM 11/25/00 -0700, Ron Chmara wrote: >Note: CC'd to Hackers, as this has wandered into deeper feature issues. > >Tom Lane wrote: >> GH <grasshacker@over-yonder.net> writes: >> > Do the "persistent-connected" Postgres backends ever timeout or die? >> No. A backend will sit patiently for the client to send it another >> query or close the connection. > >This does have an unfortunate denial-of-service implication, where >an attack can effectively suck up all available backends, and there's >no throttle, no timeout, no way of automatically dropping these.... > >However, the more likely possibility is similar to the problem that >we see in PHP's persistant connections.... a normally benign connection >is inactive, and yet it isn't dropped. If you have two of these created >every day, and you only have 16 backends, after 8 days you have a lockout. > >On a busy web site or another busy application, you can, of course, >exhaust 64 backends in a matter of minutes. Ugh...the more I read stuff like this the more I appreciate AOlserver's built-in database API which protects the application from any such problems altogether. The particular problem being described simply can't occur in this environment. - Don Baccus, Portland OR <dhogaza@pacifier.com> Nature photos, on-line guides, Pacific Northwest Rare Bird Alert Service and other goodies at http://donb.photo.net.
I've tried quite a bit to use persistent connections with PHP (for over a year) and always the scripts that I try to use them with behave crazy... The last time I tried there were problems all over the place with PHP, variables getting overwritten, certain functions just totally breaking (date() to name one) and so on.. I know I'm not being specific but my point is that I think there are some other outstanding PHP issues that play into this problem as the behavior that I've seen isn't directly related to PostgreSQL but only happens when I use persistent connections.. I've been trying to corner the problem for quite some time, it's an elusive one for sure.. I spoke with the PHP developers 9 or so months ago about the problems and they didn't seem to pay any attention to it, the thread on the mailing list was short with the bug report collecting dust at the bottom of the to-do list I'm sure (as that was back before PHP 4 was even released and obviously the problem remains).. Just my $0.02 worth. -Mitch ----- Original Message ----- From: "Ron Chmara" <ron@Opus1.COM> To: "Tom Lane" <tgl@sss.pgh.pa.us>; "PostgreSQL Hackers List" <pgsql-hackers@postgresql.org> Cc: "GH" <grasshacker@over-yonder.net>; <pgsql-novice@postgresql.org> Sent: Saturday, November 25, 2000 4:26 PM Subject: [HACKERS] Re: [NOVICE] Re: re : PHP and persistent connections > Note: CC'd to Hackers, as this has wandered into deeper feature issues. > > Tom Lane wrote: > > GH <grasshacker@over-yonder.net> writes: > > > Do the "persistent-connected" Postgres backends ever timeout or die? > > No. A backend will sit patiently for the client to send it another > > query or close the connection. > > This does have an unfortunate denial-of-service implication, where > an attack can effectively suck up all available backends, and there's > no throttle, no timeout, no way of automatically dropping these.... > > However, the more likely possibility is similar to the problem that > we see in PHP's persistant connections.... a normally benign connection > is inactive, and yet it isn't dropped. If you have two of these created > every day, and you only have 16 backends, after 8 days you have a lockout. > > On a busy web site or another busy application, you can, of course, > exhaust 64 backends in a matter of minutes. > > > > Is it possible to set something like a timeout for persistent connctions? > > > (Er, would that be something that someone would want > > > to do? A Bad Thing?) > > This has been suggested before, but I don't think any of the core > > developers consider it a good idea. Having the backend arbitrarily > > disconnect on an active client would be a Bad Thing for sure. > > Right.... but I don't think anybody has suggested disconnecting an *active* > client, just inactive ones. > > > Hence, > > any workable timeout would have to be quite large (order of an > > hour, maybe? not milliseconds anyway). > > The mySQL disconnect starts at around 24 hours. It prevents a slow > accumulation of unused backends, but does nothing for a rapid > accumulation. It can be cranked down to a few minutes AFAIK. > > > And that means that it's not > > an effective solution for the problem. Under load, a webserver that > > wastes backend connections will run out of available backends long > > before a safe timeout would start to clean up after it. > > Depends on how it's set up... you see, this isn't uncharted territory, > other web/db solutions have already fought with this issue. Much > like the number of backends set up for pgsql must be static, a timeout > may wind up being the same way. The critical thing to realize is > that you are timing out _inactive_ connections, not connections > in general. So provided that a connection provided information > about when it was last used, or usage set a counter somewhere, it > could easily be checked. > > > To my mind, a client app that wants to use persistent connections > > has got to implement some form of connection pooling, so that it > > recycles idle connections back to a "pool" for allocation to task > > threads that want to make a new query. And the threads have to release > > connections back to the pool as soon as they're done with a transaction. > > Actively releasing an idle connection is essential, rather than > > depending on a timeout. > > > > I haven't studied PHP at all, but from this conversation I gather that > > it's only halfway there... > > Well...... This is exactly how apache and PHP serve pages. The > problem is that apache children aren't threads, they are separate copies > of the application itself. So a single apache thread will re-use the > same connection, over and over again, and give that conection over to > other connections on that apache thread.. so in your above model, it's > not really one client application in the first place. > > It's a dynamic number of client applications, between one and hundreds > or so. > > So to turn the feature request the other way 'round: > "I have all sorts of client apps, connecting in different ways, to > my server. Some of the clients are leaving their connections open, > but unused. How can I prevent running out of backends, and boot > the inactive users off?" > > -Ronabop > > -- > Brought to you from iBop the iMac, a MacOS, Win95, Win98, LinuxPPC machine, > which is currently in MacOS land. Your bopping may vary. >
At 10:00 PM 11/25/00 -0800, Mitch Vincent wrote: > I've tried quite a bit to use persistent connections with PHP (for over >a year) and always the scripts that I try to use them with behave crazy... >The last time I tried there were problems all over the place with PHP, >variables getting overwritten, certain functions just totally breaking >(date() to name one) and so on.. I know I'm not being specific but my point >is that I think there are some other outstanding PHP issues that play into >this problem as the behavior that I've seen isn't directly related to >PostgreSQL but only happens when I use persistent connections.. I've heard rumors that PHP isn't thoroughly threadsafe, could this be a source of your problems? - Don Baccus, Portland OR <dhogaza@pacifier.com> Nature photos, on-line guides, Pacific Northwest Rare Bird Alert Service and other goodies at http://donb.photo.net.
I'm sure that this, if true, could certainly be the source of the problems I've seen... I can't comment on if PHP is completely threadsafe, I know that some of the modules (for lack of a better word) aren't, possible the ClibPDF library I'm using. I'll check into it. Thanks! -Mitch ----- Original Message ----- From: "Don Baccus" <dhogaza@pacifier.com> To: "Mitch Vincent" <mitch@venux.net>; "PostgreSQL Hackers List" <pgsql-hackers@postgresql.org> Cc: <pgsql-novice@postgresql.org> Sent: Saturday, November 25, 2000 9:18 PM Subject: Re: [HACKERS] Re: [NOVICE] Re: re : PHP and persistent connections > At 10:00 PM 11/25/00 -0800, Mitch Vincent wrote: > > I've tried quite a bit to use persistent connections with PHP (for over > >a year) and always the scripts that I try to use them with behave crazy... > >The last time I tried there were problems all over the place with PHP, > >variables getting overwritten, certain functions just totally breaking > >(date() to name one) and so on.. I know I'm not being specific but my point > >is that I think there are some other outstanding PHP issues that play into > >this problem as the behavior that I've seen isn't directly related to > >PostgreSQL but only happens when I use persistent connections.. > > I've heard rumors that PHP isn't thoroughly threadsafe, could this be a > source of your problems? > > > > > - Don Baccus, Portland OR <dhogaza@pacifier.com> > Nature photos, on-line guides, Pacific Northwest > Rare Bird Alert Service and other goodies at > http://donb.photo.net. >
You could set MaxRequestsPerChild in apache's httpd.conf. This controls how many requests each apache process is allowed to serve. After it serves this many the process dies which should close the postgres process as well (if it isn't, you have other problems). I know that for a long time Apache recommened setting this fairly low on Solaris due to a memory leak in solaris...ideally you'd want to set this really high, but setting it low will make the processes die... -philip On Fri, 24 Nov 2000, jmcazurin wrote: > > At 12:47 PM 11/24/00, GH wrote: > >On Fri, Nov 24, 2000 at 03:17:59PM +1100, some SMTP stream spewed forth: > > > Oh, and if you are using pg_close() I don't think it works > > > in any currently released PHP4 versions. See: > > > >This seems to be true. I ran into some fun link errors while > >connecting and disconnecting more than once in a script. > > This sounds disturbing! > > How then should I go about closing persistent connections? Can I close > them at all? > > Would pg_close() work if I used it on non-persistent connections? > > Thanks in advance, > > Mikah >
> Is it possible to set something like a timeout for persistent connctions? > (Er, would that be something that someone would want > to do? A Bad Thing?) see my other email about apache's MaxRequestsPerChild... > What happens when the httpd process that held a persistent connection > dies? Does "its" postgres process drop the connection and wait for > others? When the spare apache processes die, the postgres processes > remain. On my server (freebsd 4.x, php 4.0.2, postgresl 7.0.3) when I kill the httpd processes the postgres processes die as well...