Re: [PERFORM] database slowdown while a lot of inserts occur
Few words regarding small inserts and a lot of fsyncs: If it is your problem, you can fix this by using battery-backed raid card. Similar effect can be reached by turning synchronious commit off. Note that the latter may make few last commits lost in case of sudden reboot. But you can at least test if moving to BBU will help you. (Dunno if this setting can be changed with SIGHUP without restart). Note that this may still be a lot of random writes. And in case of RAID5 - a lot of random reads too. I don't think batching will help other applications. This is the tool to help application that uses batching. If you have random writes, look at HOT updates - they may help you if you will follow requirements. Check your checkpoints - application writes to commit log first (sequential write), then during checkpoints data is written to tables (random writes) - longer checkpoints may make you life easier. Try to increase checkpoint_segments. If you have alot of data written - try to move you commit logs to another drive/partition. If you have good raid card with memory and BBU, you may try to disable read cache on it (leaving only write cache). Read cache is usually good at OS level (with much more memory) and fast writes need BBU-protected write cache. Best regards, Vitalii Tymchyshyn 2012/3/29 Campbell, Lance > PostgreSQL 9.0.x > > We have around ten different applications that use the same database. > When one particular application is active it does an enormous number of > inserts. Each insert is very small. During this time the database seems > to slow down in general. The application in question is inserting into a > particular table that is not used by the other applications. > > ** ** > > **1) **What should I do to confirm that the database is the issue > and not the applications? > > **2) **How can I identify where the bottle neck is occurring if the > issue happens to be with the database? > > ** ** > > I have been using PostgreSQL for eight years. It is an amazing database.* > *** > > ** ** > > Thanks, > > ** ** > > Lance Campbell > > Software Architect > > Web Services at Public Affairs > > 217-333-0382 > > ** ** > -- Best regards, Vitalii Tymchyshyn
Re: [PERFORM] TCP Overhead on Local Loopback
On Sun, Apr 1, 2012 at 6:11 PM, Andrew Dunstan wrote: > > > On 04/01/2012 08:29 PM, Claudio Freire wrote: > >> On Sun, Apr 1, 2012 at 8:54 PM, Andrew Dunstan >> wrote: >> >>> You could try using Unix domain socket and see if the performance improves. A relevant link: >>> >>> He said Windows. There are no Unix domain sockets on Windows. (And please >>> don't top-post) >>> >> Windows supports named pipes, which are functionally similar, but I >> don't think pg supports them. >> >> > Correct, so telling the OP to have a look at them isn't at all helpful. > And they are not supported on all Windows platforms we support either > (specifically not on XP, AIUI). > But suggesting moving away from TCP/IP with no actual evidence that it is network overhead that is the problem is a little premature, regardless. What, exactly, are the set of operations that each update is performing and is there any way to batch them into fewer statements within the transaction. For example, could you insert all 60,000 records into a temporary table via COPY, then run just a couple of queries to do bulk inserts and bulk updates into the destination tble via joins to the temp table? 60,000 rows updated with 25 columns, 1 indexed in 3ms is not exactly slow. That's a not insignificant quantity of data which must be transferred from client to server, parsed, and then written to disk, regardless of TCP overhead. That is happening via at least 60,000 individual SQL statements that are not even prepared statements. I don't imagine that TCP overhead is really the problem here. Regardless, you can reduce both statement parse time and TCP overhead by doing bulk inserts (COPY) followed by multi-row selects/updates into the final table. I don't know how much below 3ms you are going to get, but that's going to be as fast as you can possibly do it on your hardware, assuming the rest of your configuration is as efficient as possible.
Re: [PERFORM] TCP Overhead on Local Loopback
On 04/01/2012 09:11 PM, Andrew Dunstan wrote: On 04/01/2012 08:29 PM, Claudio Freire wrote: On Sun, Apr 1, 2012 at 8:54 PM, Andrew Dunstan wrote: You could try using Unix domain socket and see if the performance improves. A relevant link: He said Windows. There are no Unix domain sockets on Windows. (And please don't top-post) Windows supports named pipes, which are functionally similar, but I don't think pg supports them. Correct, so telling the OP to have a look at them isn't at all helpful. And they are not supported on all Windows platforms we support either (specifically not on XP, AIUI). Apparently I was mistaken about the availability. However, my initial point remains. Since all our client/server comms on Windows are over TCP, telling the OP to look at Unix domain sockets is unhelpful. cheers andrew -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] TCP Overhead on Local Loopback
On Sun, Apr 1, 2012 at 1:24 PM, Ofer Israeli wrote: > Hi all, > > We are running performance tests using PG 8.3 on a Windows 2008 R2 machine > connecting locally over TCP. > In our tests, we have found that it takes ~3ms to update a table with ~25 > columns and 60K records, with one column indexed. I assume you mean 3ms per row, as per 3ms per 60,000 rows (or per 5,000 rows?) seems improbably fast. > We have reached this number after many tweaks of the database configuraiton > and one of the changes we made was to perform the updates in batches of 5K > as opposed to the pervious transaction per event. Note that our use of > batches is to have only one transaction, but still each of the 5K events is > independently SELECTing and UPDATEing records, i.e. it is not all contained > in a stored procedure or such. > > Still these times are too high for us and we are looking to lower them and I > am wondering about the TCP/IP overhead of passing the information back and > forth. Does anyone have any numbers in what the TCP could cost in the > configuration mentioned above or pointers on how to test it? Change all your updates to selects, with the same where clause. If doing that makes it much faster, TCP must not have been your bottleneck. Cheers, Jeff -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
