Re: [h2] Poor performance
That's improved things greatly for my test cases, thanks! On Saturday, December 26, 2015 at 7:35:43 AM UTC-5, Noel Grandin wrote: > > I have puhed a fix for this to master. Please try it out and let me > know how it works for you. > > The fix changes the index costing quite a bit, so it might affect > other queries too. > -- You received this message because you are subscribed to the Google Groups "H2 Database" group. To unsubscribe from this group and stop receiving emails from it, send an email to h2-database+unsubscr...@googlegroups.com. To post to this group, send email to h2-database@googlegroups.com. Visit this group at https://groups.google.com/group/h2-database. For more options, visit https://groups.google.com/d/optout.
Re: [h2] Poor performance
I have puhed a fix for this to master. Please try it out and let me know how it works for you. The fix changes the index costing quite a bit, so it might affect other queries too. -- You received this message because you are subscribed to the Google Groups "H2 Database" group. To unsubscribe from this group and stop receiving emails from it, send an email to h2-database+unsubscr...@googlegroups.com. To post to this group, send email to h2-database@googlegroups.com. Visit this group at https://groups.google.com/group/h2-database. For more options, visit https://groups.google.com/d/optout.
Re: [h2] Poor performance
James, I think query optimizer hints would really help here. Unfortunately, no one has offered to implement them yet, I think. On Wednesday, 23 December 2015 18:07:00 UTC+1, James Sheets wrote: > > Just to be clear, by "covering" I meant an index that covers the predicate > and the projection. > -- You received this message because you are subscribed to the Google Groups "H2 Database" group. To unsubscribe from this group and stop receiving emails from it, send an email to h2-database+unsubscr...@googlegroups.com. To post to this group, send email to h2-database@googlegroups.com. Visit this group at https://groups.google.com/group/h2-database. For more options, visit https://groups.google.com/d/optout.
Re: [h2] Poor performance
Just to be clear, by "covering" I meant an index that covers the predicate and the projection. -- You received this message because you are subscribed to the Google Groups "H2 Database" group. To unsubscribe from this group and stop receiving emails from it, send an email to h2-database+unsubscr...@googlegroups.com. To post to this group, send email to h2-database@googlegroups.com. Visit this group at https://groups.google.com/group/h2-database. For more options, visit https://groups.google.com/d/optout.
Re: [h2] Poor performance
Yes, but there's a very large real-world performance difference between using the index I've created and the unique key that H2 chooses. I don't know anything about the internals of H2, but I could make some guesses as to why. I personally think the most intuitive behavior would be to use a covering index over a PK or UK that doesn't cover. Unique Key index is *422 ms* -- Performance SELECT MAX(b.id) as id FROM tbl_b b GROUP BY b.tbl_a_id [2015-12-23 11:38:17] 100 rows retrieved starting from 1 in 422ms (execution: 410ms, fetching: 12ms) -- Explain Analyze SELECT MAX(B.ID) AS ID FROM PUBLIC.TBL_B B /* PUBLIC.TBL_B_UK_INDEX_4 */ /* scanCount: 5 */ GROUP BY B.TBL_A_ID /* group sorted */ /* reads: 31554 */ The TBL_B_IDX is *58 ms* -- Performance SELECT MAX(b.id) as id FROM tbl_b b -- This where predicate is just to trick H2 to using tbl_b_idx WHERE b.tbl_a_id > 0 GROUP BY b.tbl_a_id [2015-12-23 11:44:50] 100 rows retrieved starting from 1 in 58ms (execution: 50ms, fetching: 8ms) -- Explain Analyze SELECT MAX(B.ID) AS ID FROM PUBLIC.TBL_B B /* PUBLIC.TBL_B_IDX: TBL_A_ID > 0 */ /* scanCount: 5 */ WHERE B.TBL_A_ID > 0 GROUP BY B.TBL_A_ID On Tuesday, December 22, 2015 at 1:12:18 AM UTC-5, Noel Grandin wrote: > > > > On 2015-12-22 05:28 AM, James Sheets wrote: > > Try making another unit test, checking that the below query uses > 'tbl_b_idx', and the test case will fail: > > > > EXPLAIN ANALYZE > > SELECT MAX(b.id)as id > > FROM tbl_b b > > GROUP BY b.tbl_a_id; > > > > For this particular query, you need to read all of the rows, so there is > no cost difference in using one index over another. > -- You received this message because you are subscribed to the Google Groups "H2 Database" group. To unsubscribe from this group and stop receiving emails from it, send an email to h2-database+unsubscr...@googlegroups.com. To post to this group, send email to h2-database@googlegroups.com. Visit this group at https://groups.google.com/group/h2-database. For more options, visit https://groups.google.com/d/optout.
Re: [h2] Poor performance
On 2015-12-22 05:28 AM, James Sheets wrote: Try making another unit test, checking that the below query uses 'tbl_b_idx', and the test case will fail: EXPLAIN ANALYZE SELECT MAX(b.id)as id FROM tbl_b b GROUP BY b.tbl_a_id; For this particular query, you need to read all of the rows, so there is no cost difference in using one index over another. -- You received this message because you are subscribed to the Google Groups "H2 Database" group. To unsubscribe from this group and stop receiving emails from it, send an email to h2-database+unsubscr...@googlegroups.com. To post to this group, send email to h2-database@googlegroups.com. Visit this group at https://groups.google.com/group/h2-database. For more options, visit https://groups.google.com/d/optout.
Re: [h2] Poor performance
Thanks! I tried out your changes, and it's made some improvement. The query I originally submitted does seem to use the correct index. However, if you just slightly modify the test query (which I see you made a unit test for), the same issue comes back up. Try making another unit test, checking that the below query uses 'tbl_b_idx', and the test case will fail: EXPLAIN ANALYZE SELECT MAX(b.id) as id FROM tbl_b b GROUP BY b.tbl_a_id; On Sunday, December 20, 2015 at 9:19:06 AM UTC-5, Noel Grandin wrote: > > I have committed a fix for this to master. You can either build from > source or try out the nightly build later > -- You received this message because you are subscribed to the Google Groups "H2 Database" group. To unsubscribe from this group and stop receiving emails from it, send an email to h2-database+unsubscr...@googlegroups.com. To post to this group, send email to h2-database@googlegroups.com. Visit this group at https://groups.google.com/group/h2-database. For more options, visit https://groups.google.com/d/optout.
Re: [h2] Poor performance
I have committed a fix for this to master. You can either build from source or try out the nightly build later -- You received this message because you are subscribed to the Google Groups "H2 Database" group. To unsubscribe from this group and stop receiving emails from it, send an email to h2-database+unsubscr...@googlegroups.com. To post to this group, send email to h2-database@googlegroups.com. Visit this group at https://groups.google.com/group/h2-database. For more options, visit https://groups.google.com/d/optout.
Re: [h2] Poor performance
I added some debug and this is the output: 2015-12-19 14:36:15 jdbc[3]: Plan : calculate cost for plan [B, A] 2015-12-19 14:36:15 jdbc[3]: Plan : for table filter B 2015-12-19 14:36:15 jdbc[3]: Table : potential plan item cost 509,990 index PUBLIC.TBL_B.tableScan 2015-12-19 14:36:15 jdbc[3]: Table : potential plan item cost 509,990 index PUBLIC.PRIMARY_KEY_4B 2015-12-19 14:36:15 jdbc[3]: Table : potential plan item cost 509,990 index PUBLIC.TBL_B_UK_INDEX_4 2015-12-19 14:36:15 jdbc[3]: Table : potential plan item cost 509,990 index PUBLIC.TBL_B_IDX 2015-12-19 14:36:15 jdbc[3]: Plan : best plan item cost 504,890 index PUBLIC.TBL_B.tableScan 2015-12-19 14:36:15 jdbc[3]: Plan : for table filter A 2015-12-19 14:36:15 jdbc[3]: Table : potential plan item cost 11,000 index PUBLIC.TBL_A.tableScan 2015-12-19 14:36:15 jdbc[3]: Table : potential plan item cost 30 index PUBLIC.PRIMARY_KEY_4 2015-12-19 14:36:15 jdbc[3]: Table : potential plan item cost 11,000 index PUBLIC.TBL_A_UK_INDEX_4 2015-12-19 14:36:15 jdbc[3]: Plan : best plan item cost 29 index PUBLIC.PRIMARY_KEY_4 2015-12-19 14:36:15 jdbc[3]: Plan : plan cost 15,500,156 2015-12-19 14:36:15 jdbc[3]: Plan : calculate cost for plan [A, B] 2015-12-19 14:36:15 jdbc[3]: Plan : for table filter A 2015-12-19 14:36:15 jdbc[3]: Table : potential plan item cost 11,000 index PUBLIC.TBL_A.tableScan 2015-12-19 14:36:15 jdbc[3]: Table : potential plan item cost 11,000 index PUBLIC.PRIMARY_KEY_4 2015-12-19 14:36:15 jdbc[3]: Table : potential plan item cost 11,000 index PUBLIC.TBL_A_UK_INDEX_4 2015-12-19 14:36:15 jdbc[3]: Plan : best plan item cost 10,780 index PUBLIC.TBL_A.tableScan 2015-12-19 14:36:15 jdbc[3]: Plan : for table filter B 2015-12-19 14:36:15 jdbc[3]: Table : potential plan item cost 509,990 index PUBLIC.TBL_B.tableScan 2015-12-19 14:36:15 jdbc[3]: Table : potential plan item cost 509,990 index PUBLIC.PRIMARY_KEY_4B 2015-12-19 14:36:15 jdbc[3]: Table : potential plan item cost 1,020 index PUBLIC.TBL_B_UK_INDEX_4 2015-12-19 14:36:15 jdbc[3]: Table : potential plan item cost 1,020 index PUBLIC.TBL_B_IDX 2015-12-19 14:36:15 jdbc[3]: Plan : best plan item cost 1,014 index PUBLIC.TBL_B_UK_INDEX_4 2015-12-19 14:36:15 jdbc[3]: Plan : plan cost 10,952,417 The interesting part is the following two lines: 2015-12-19 14:36:15 jdbc[3]: Table : potential plan item cost 1,020 index PUBLIC.TBL_B_UK_INDEX_4 2015-12-19 14:36:15 jdbc[3]: Table : potential plan item cost 1,020 index PUBLIC.TBL_B_IDX which means that our index cost calculation does not know how to take into account that retrieving from a primary key index is way cheaper than retrieving from any other index. -- You received this message because you are subscribed to the Google Groups "H2 Database" group. To unsubscribe from this group and stop receiving emails from it, send an email to h2-database+unsubscr...@googlegroups.com. To post to this group, send email to h2-database@googlegroups.com. Visit this group at https://groups.google.com/group/h2-database. For more options, visit https://groups.google.com/d/optout.
Re: [h2] Poor performance
This is the output of EXPLAIN ANALYZE for me: EXPLAIN ANALYZE SELECT MAX(b.id) as id FROM tbl_b b JOIN tbl_a a ON b.tbl_a_id = a.id GROUP BY b.tbl_a_id HAVING a.active = true; PLAN SELECT MAX(B.ID) AS ID FROM PUBLIC.TBL_A A /* PUBLIC.TBL_A.tableScan */ /* scanCount: 101 */ INNER JOIN PUBLIC.TBL_B B /* PUBLIC.TBL_B_UK_INDEX_4: TBL_A_ID = A.ID */ ON 1=1 /* scanCount: 50099 */ WHERE B.TBL_A_ID = A.ID GROUP BY B.TBL_A_ID HAVING A.ACTIVE = TRUE /* total: 892 TBL_B.TBL_B_DATA read: 614 (68%) TBL_B.TBL_B_UK_INDEX_4 read: 278 (31%) */ (1 row, 229 ms) EXPLAIN ANALYZE SELECT MAX(b.id) as id FROM tbl_b b JOIN tbl_a a ON b.tbl_a_id = a.id GROUP BY b.tbl_a_id HAVING a.active = true; PLAN SELECT MAX(B.ID) AS ID FROM PUBLIC.TBL_A A /* PUBLIC.TBL_A.tableScan */ /* scanCount: 101 */ INNER JOIN PUBLIC.TBL_B B /* PUBLIC.TBL_B_IDX: TBL_A_ID = A.ID */ ON 1=1 /* scanCount: 50099 */ WHERE B.TBL_A_ID = A.ID GROUP BY B.TBL_A_ID HAVING A.ACTIVE = TRUE /* TBL_B.TBL_B_IDX read: 46 */ (1 row, 25 ms) -- You received this message because you are subscribed to the Google Groups "H2 Database" group. To unsubscribe from this group and stop receiving emails from it, send an email to h2-database+unsubscr...@googlegroups.com. To post to this group, send email to h2-database@googlegroups.com. Visit this group at https://groups.google.com/group/h2-database. For more options, visit https://groups.google.com/d/optout.
