Re: [HACKERS] why after increase the hash table partitions, TPMC decrease
On Wed, Sep 3, 2014 at 8:44 AM, Xiaoyulei xiaoyu...@huawei.com wrote: benchmarSQL has about half reads. So I think it should be effective. I don't think BufFreelistLock take much time, it just get a buffer from list. It should be very fast. Only incase all the data fits in shared buffers, else it needs to perform clock sweep which can be costly in certain cases. The test server has 2 CPUs and 12 cores in each CPU. 24 processor totally. CPU Idle time is over 50%. IO only 10%(data is in SSD) I perf one process of pg. The hot spot is hash search. perf data file is more than 1M, so I do not attach it. I send it separately. Could you once check the callers of hash_search_with_hash_value() as it gets called from multiple paths? I am not able to view the perf.data file you have sent. Also, you might want to check the performance on 9.4 codebase, as there are quite a few performance improvements in it. With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
Re: [HACKERS] why after increase the hash table partitions, TPMC decrease
On Tue, Sep 2, 2014 at 2:09 PM, Xiaoyulei xiaoyu...@huawei.com wrote: We use benchmarksql to start tpcc test in postgresql 9.3.3. Before test we set benchmarksql client number about 800. And we increase the hash partitions from 16 to 1024 , in order to reduce the hash partition locks competition. We expect that after increase the number of partitions, reduces lock competition, TPMC should be increased. I think you can expect some increase mainly if your test is read only and you have sufficient RAM such that it can contain all the data, for other cases there can be I/O due to which you might not see any increase. But the test results on the contrary, after modified to 1024, TPMC did not increase, but decrease. Why such result? We modify the following macro definition: NUM_BUFFER_PARTITIONS 1024 LOG2_NUM_PREDICATELOCK_PARTITIONS 10 LOG2_NUM_LOCK_PARTITIONS 10 Increasing these numbers might lead to error too many LWLocks taken, unless you increase MAX_SIMUL_LWLOCKS. Once you can check the server log if it contains any errors, that might lead to decrease in performance. Also another side effect would be that increasing above numbers will lead to increase in shared memory usage. With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
Re: [HACKERS] why after increase the hash table partitions, TPMC decrease
On Tue, Sep 2, 2014 at 1:39 AM, Xiaoyulei xiaoyu...@huawei.com wrote: We use benchmarksql to start tpcc test in postgresql 9.3.3. Before test we set benchmarksql client number about 800. And we increase the hash partitions from 16 to 1024 , in order to reduce the hash partition locks competition. Can you give the complete invocation parameters for benchmarksql? How many CPUs/cores do you have? We expect that after increase the number of partitions, reduces lock competition, TPMC should be increased. But the test results on the contrary, after modified to 1024, TPMC did not increase, but decrease. Why such result? Increasing the partition numbers would only help with contention that is due to hash collision. If all of the contention is on, for example, the root block of one index, then increasing the number partitions won't change that, because that block is always going to map to a single partition. Can you perf or some other profiling tool to find where your bottleneck is? Cheers, Jeff
Re: [HACKERS] why after increase the hash table partitions, TPMC decrease
benchmarSQL has about half reads. So I think it should be effective. I don't think BufFreelistLock take much time, it just get a buffer from list. It should be very fast. The test server has 2 CPUs and 12 cores in each CPU. 24 processor totally. CPU Idle time is over 50%. IO only 10%(data is in SSD) I perf one process of pg. The hot spot is hash search. perf data file is more than 1M, so I do not attach it. I send it separately. 3.63% postgres postgres [.] hash_search_with_hash_value 3.10% postgres postgres [.] AllocSetAlloc 3.04% postgres postgres [.] LWLockAcquire 2.73% postgres postgres [.] _bt_compare 2.66% postgres postgres [.] SearchCatCache 2.18% postgres postgres [.] ExecInitExpr 2.11% postgres postgres [.] GetSnapshotData 1.57% postgres postgres [.] PinBuffer 1.41% postgres postgres [.] XLogInsert 1.36% postgres libc-2.11.3.so [.] _int_malloc 1.31% postgres postgres [.] LWLockRelease 1.09% postgres libc-2.11.3.so [.] __GI_memcpy 0.89% postgres postgres [.] _bt_checkkeys 0.82% postgres libc-2.11.3.so [.] __strncpy_ssse3 0.81% postgres postgres [.] palloc 0.81% postgres postgres [.] fmgr_info_cxt_security 0.76% postgres postgres [.] equal 0.75% postgres postgres [.] s_lock 0.73% postgres postgres [.] heap_hot_search_buffer From: Amit Kapila [mailto:amit.kapil...@gmail.com] Sent: Tuesday, September 02, 2014 10:44 PM To: Xiaoyulei Cc: pgsql-hackers@postgresql.org Subject: Re: 答复: [HACKERS] why after increase the hash table partitions, TPMC decrease On Tue, Sep 2, 2014 at 5:20 PM, Xiaoyulei xiaoyu...@huawei.com wrote: I already modified MAX_SIMUL_LWLOCKS to make sure it is enough. Okay. Total RAM is 130G, and I set shared_buffers 16G, CPU and IO is not full. 50% CPUs are idle. As far as I understand, benchmarkSQL measures an OLTP workload performance which means it contains mix of reads and writes, now I am not sure how you have identified that increasing buffer partitions can improve the performance. Have you used any profiling? So
