Thread: BUG #6311: Performance degradation after upgrade
The following bug has been logged online: Bug reference: 6311 Logged by: Roye Cohen Email address: roye.cohen@sap.com PostgreSQL version: 9.1.1 Operating system: Linux Redhat Description: Performance degradation after upgrade Details: Hi, I am a performance engineer. I was conducting a comparison from postgres 9.0 to 9.1.1 in order to upgrade to the newest version. I found a degradation in physical memory used on DB server (~200% degradation) and a small degradation in response times on every transaction monitored in comparison to 9.0. The test was done on HP LoadRunner with 300 concurrent users executing a flow of events. â¢The exact sequence of steps is hard to describe but it is important to state that the executions were exactly the same. Default postgres settings were used (settings were not changed after installing postgres). OS Version: Linux 2.6.18-164.el5 x86_64 I am at your service if you have any further inqueries. Best regards, Roye
Roye Cohen wrote: > > The following bug has been logged online: > > Bug reference: 6311 > Logged by: Roye Cohen > Email address: roye.cohen@sap.com > PostgreSQL version: 9.1.1 > Operating system: Linux Redhat > Description: Performance degradation after upgrade > Details: > > Hi, > > I am a performance engineer. I was conducting a comparison from postgres 9.0 > to 9.1.1 in order to upgrade to the newest version. > I found a degradation in physical memory used on DB server (~200% > degradation) and a small degradation in response times on every transaction > monitored in comparison to 9.0. I am confused by the word "degradation". You mean that Postgres 9.1 used 3x more memory than PG 9.0? How much slower was it? > The test was done on HP LoadRunner with 300 concurrent users executing a > flow of events. > > The exact sequence of steps is hard to describe but it is important to > state that the executions were exactly the same. Default postgres settings > were used (settings were not changed after installing postgres). > > > OS Version: Linux 2.6.18-164.el5 x86_64 > > I am at your service if you have any further inqueries. We have certainly never heard of a report like this between PG 9.0 and 9.1, so I am confused. Was their any change in the client interface software between the two tests? -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. +
"Roye Cohen" wrote: > I found a degradation in physical memory used on DB server (~200% > degradation) What are you measuring, and what were the numbers? > and a small degradation in response times on every transaction > monitored in comparison to 9.0. What transaction isolation level was used? Since you have a sap.com email address, I assume you're probably oriented to larger shops, which in my experience are more inclined to use stricter transaction isolation levels (for very good reasons, IMV). If the transactions were set to the SERIALIZABLE transaction isolation level, we would expect slightly slower performance in 9.1 versus 9.0, because it now provides truly serializable behavior, unlike earlier versions of PostgreSQL or any production release of Oracle. If this is the case, you can fall back to legacy behavior by using the REPEATABLE READ transaction isolation level instead of SERIALIZABLE. For further information see these links: http://www.postgresql.org/docs/9.1/interactive/transaction-iso.html http://wiki.postgresql.org/wiki/SSI If this is the cause, please let us know. I would appreciate knowing what kind of numbers you're seeing, with a description of the type of load. If you can confirm that this is not happening at a less strict transaction isolation level, like REPEATABLE READ, we can clear this as "not a bug", since you don't get truly serializable transactions without cost -- that's why less strict levels exist. -Kevin