Re: Buffer Requests Trace - Mailing list pgsql-hackers
| From | Lucas Lersch |
|---|---|
| Subject | Re: Buffer Requests Trace |
| Date | |
| Msg-id | CAGR3jZCT-40VArPx_CEqN7HFOp55VJsRW6Hz75ofxKSOo94j8g@mail.gmail.com Whole thread Raw |
| In response to | Re: Buffer Requests Trace (Jeff Janes <jeff.janes@gmail.com>) |
| List | pgsql-hackers |
Answering your first question: running tpcc for 1 minute, in a database with 64 warehouses (6~7GB), with a buffer pool of 128MB (around 1.8% of database size) and a hit ratio of ~91%, I get a throughput of 45~50 transactions per second.
Table | Index | Data Size | Index Size | Total
------------+--------------------------------------+-----------+------------+---------
stock | stock_pkey | 2209 MB | 263 MB | 2472 MB
order_line | order_line_pkey | 2041 MB | 678 MB | 2719 MB
customer | idx_customer_name | 1216 MB | 146 MB | 1420 MB
customer | customer_pkey | 1216 MB | 58 MB | 1420 MB
history | | 164 MB | | 164 MB
oorder | oorder_pkey | 134 MB | 68 MB | 362 MB
oorder | idx_order | 134 MB | 80 MB | 362 MB
oorder | oorder_o_w_id_o_d_id_o_c_id_o_id_key | 134 MB | 80 MB | 362 MB
new_order | new_order_pkey | 27 MB | 17 MB | 45 MB
item | item_pkey | 10168 kB | 2208 kB | 12 MB
district | district_pkey | 776 kB | 72 kB | 880 kB
warehouse | warehouse_pkey | 384 kB | 16 kB | 432 kB
By executing the tpcc benchmark for 1 minute I get about 2.9 million buffer requests. The distribution of these requests in the relations and indexes are (in descending order):
customer 1383399
stock_pkey 442600
stock 321370
order_line 255314
order_line_pkey 156132
oorder 58665
oorder_pkey 57895
customer_pkey 44471
new_order_pkey 39552
idx_customer_name 28286
new_order 25861
item_pkey 11702
item 11606
district 11389
district_pkey 7575
warehouse 5276
idx_order 4072
oorder_o_w_id_o_d_id_o_c_id_o_id_key 2410
warehouse_pkey 1998
history 1958
All this information seems normal to me. However, from the 2.9 million buffer requests over ~800k pages, only ~150k distinct pages are being requested. This behavior could be explained by the benchmark accessing only a small set of the 64 warehouses instead of having a normal distributed access over the 64 warehouses. In other words, I think that the execution time of the benchmark is irrelevant, assuming that the transactions follow a normal distribution regarding accesses to warehouses.
On Wed, Oct 15, 2014 at 7:41 PM, Jeff Janes <jeff.janes@gmail.com> wrote:
On Wed, Oct 15, 2014 at 6:22 AM, Lucas Lersch <lucaslersch@gmail.com> wrote:So is it a possible normal behavior that running tpcc for 10min only access 50% of the database? Furthermore, is there a guideline of parameters for tpcc (# of warehouses, execution time, operations weight)?I'm not familiar with your benchmarking tool. With the one I am most familiar with, pgbench, if you run it against a database which is too big to fit in memory, it can take a very long time to touch each page once, because the constant random disk reads makes it run very slowly. Maybe that is something to consider here--how many transactions were actually executed during your 10 min run?Also, the tool might build tables that are only used under certain run options. Perhaps you just aren't choosing the options which invoke usage of those tables. Since you have the trace data, it should be pretty easy to count how many distinct blocks are accessed from each relation, and compare that to the size of the relations to see which relations are unused or lightly used.Cheers,Jeff
Lucas Lersch
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