> Thanks for the information, I will apply other patches also and > start testing. > > > When try to run the pgbench test, by default the cache-scan plan is not > chosen because of more cost. So I increased the cpu_index_tuple_cost to > a maximum value or by turning off index_scan, so that the plan can chose > the cache_scan as the least cost. > It's expected. In case of index-scan is available, its cost is obviously cheaper than cache-scan, even if it does not issue disk-i/o.
> The configuration parameters changed during the test are, > > shared_buffers - 2GB, cache_scan.num_blocks - 1024 wal_buffers - 16MB, > checkpoint_segments - 255 checkpoint_timeout - 15 min, > cpu_index_tuple_cost - 100000 or enable_indexscan=off > > Test procedure: > 1. Initialize the database with pgbench with 75 scale factor. > 2. Create the triggers on pgbench_accounts 3. Use a select query to load > all the data into cache. > 4. Run a simple update pgbench test. > > Plan details of pgbench simple update queries: > > postgres=# explain update pgbench_accounts set abalance = abalance where > aid = 100000; > QUERY PLAN > ---------------------------------------------------------------------- > ------------------------------------- > Update on pgbench_accounts (cost=0.43..100008.44 rows=1 width=103) > -> Index Scan using pgbench_accounts_pkey on pgbench_accounts > (cost=0.43..100008.44 rows=1 width=103) > Index Cond: (aid = 100000) > Planning time: 0.045 ms > (4 rows) > > postgres=# explain select abalance from pgbench_accounts where aid = > 100000; > QUERY PLAN > ---------------------------------------------------------------------- > -------------- > Custom Scan (cache scan) on pgbench_accounts (cost=0.00..99899.99 > rows=1 width=4) > Filter: (aid = 100000) > Planning time: 0.042 ms > (3 rows) > > I am observing a too much delay in performance results. The performance > test script is attached in the mail. > I want you to compare two different cases between sequential scan but part of buffers have to be loaded from storage and cache-only scan. It probably takes a difference. Thanks, -- NEC OSS Promotion Center / PG-Strom Project KaiGai Kohei <kai...@ak.jp.nec.com> -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
