Обсуждение: mis-estimate in nested query causes slow runtimes
Hello, I've been wrestling w/ a complex query for another developer for awhile today. The problem consistently seems to a mis-estimation of the number of rows resulting from a join. This causes the query early on to think it's only going to be processing 1 row and so it chooses nested loops much of the way up the chain. I've messed w/ statistics targets on some of the columns w/ no increase in the accuracy of the estimates. I've analyzed the tables in question (autovac is running). If I turn off nested loops, the query runs in 1.5 seconds. Otherwise it takes about 37s. With other criteria in the where clause it can take many minutes to return. Here is a subset of the explain analyze that I'm wrestling with. The entire explain is at the end of the email. -> Nested Loop (cost=42.74..161.76 rows=1 width=38) (actual time=2.932..27.772 rows=20153 loops=1) -> Hash Join (cost=10.89..22.58 rows=1 width=24) (actual time=0.065..0.134 rows=1 loops=1) Hash Cond: (mtchsrcprj3.funding_source_id = mtchsrcprjfs3.nameid) -> Seq Scan on project mtchsrcprj3 (cost=0.00..11.22 rows=122 width=8) (actual time=0.002..0.054 rows=122 loops=1) -> Hash (cost=10.83..10.83 rows=5 width=24) (actual time=0.017..0.017 rows=1 loops=1) -> Index Scan using name_float_lfm_idx on namemaster mtchsrcprjfs3 (cost=0.00..10.83 rows=5 width=24) (actual time=0.012..0.013 rows=1 loops=1) Index Cond: (name_float_lfm = 'DWS'::text) -> Bitmap Heap Scan on transaction_details idatrndtl (cost=31.85..121.60 rows=1407 width=22) (actual time=2.864..12.060 rows=20153 loops=1) Recheck Cond: (idatrndtl.ida_trans_match_source_id = mtchsrcprj3.id) -> Bitmap Index Scan on transaction_details_ida_trans_match_source_id (cost=0.00..31.50 rows=1407 width=0) (actual time=2.696..2.696 rows=20153 loops=1) Index Cond: (idatrndtl.ida_trans_match_source_id = mtchsrcprj3.id) The first frustration is that I can't get the transaction details scan to get any more accurate. It thinks it will find 1407 records, instead it finds 20,153. Then for whatever reason it thinks that a join between 1 record and 1407 records will return 1 record. This is mainly what I can't understand. Why does it think it will only get one record in response when it's a left join? The thing is that we've had this happen a number of times recently with complex nested queries. Most of the time things will run very quickly, but an early mis-estimation by the planner causes it to use nested loops exclusively when hash joins would be more appropriate. Is there anything I can do to improve this short of the set enable_nestloop=off? PG 8.2.4 on Linux kernel 2.6.9 x64 -Chris ------- Full explain analyze ----- Group (cost=336.76..336.82 rows=1 width=328) (actual time=36620.831..36621.176 rows=248 loops=1) -> Sort (cost=336.76..336.76 rows=1 width=328) (actual time=36620.828..36620.888 rows=248 loops=1) Sort Key: county, fullname_last_first_mdl, ((((CASE WHEN (COALESCE(fullname_last_first_mdl, '0'::text) = '0'::text) THEN ''::text ELSE COALESCE(fullname_last_first_mdl, '0'::text) END || ' '::text) || '-'::text) || ' '::text) || CASE WHEN (COALESCE(ssn, '0'::text) = '0'::text) THEN ''::text ELSE COALESCE(ssn, '0'::text) END), system_name_id, ssn, ida_account_id, ida_account_match_source_funding_source_name_float_lfm, ida_account_status, vs_query_27453_212267, vs_query_27453_212252, vs_query_27453_212253, vs_query_27453_212254, vs_query_27453_212255, (COALESCE(vs_query_27453_212267, 0::numeric) + COALESCE(vs_query_27453_212255, 0::numeric)) -> Subquery Scan foo (cost=336.72..336.75 rows=1 width=328) (actual time=36614.750..36615.319 rows=248 loops=1) -> Sort (cost=336.72..336.72 rows=1 width=255) (actual time=36614.737..36614.798 rows=248 loops=1) Sort Key: cou.validvalue, dem.name_float_lfm -> Nested Loop Left Join (cost=194.80..336.71 rows=1 width=255) (actual time=506.599..36611.702 rows=248 loops=1) -> Nested Loop Left Join (cost=194.80..332.90 rows=1 width=242) (actual time=506.566..36606.528 rows=248 loops=1) Join Filter: (acc.id = qry27453.ida_account_id) -> Nested Loop (cost=30.16..168.13 rows=1 width=82) (actual time=0.461..27.079 rows=248 loops=1) -> Nested Loop (cost=30.16..167.85 rows=1 width=90) (actual time=0.453..25.133 rows=248 loops=1) -> Nested Loop (cost=30.16..165.94 rows=1 width=77) (actual time=0.441..19.687 rows=970 loops=1) -> Nested Loop (cost=30.16..162.90 rows=1 width=40) (actual time=0.429..11.405 rows=970 loops=1) -> Hash Join (cost=30.16..162.48 rows=1 width=32) (actual time=0.417..4.524 rows=970 loops=1) Hash Cond: (accmtchgrp.match_group_id = mtchsrc2.match_group_id) -> Seq Scan on ida_account_match_sources accmtchgrp (cost=0.00..117.26 rows=3926 width=8) (actual time=0.010..1.597 rows=3933 loops=1) -> Hash (cost=30.15..30.15 rows=1 width=24) (actual time=0.315..0.315 rows=1 loops=1) - > Hash Join (cost=22.59..30.15 rows=1 width=24) (actual time=0.228..0.309 rows=1 loops=1) Hash Cond: (mtchsrc2.project_id = mtchsrcprj2.id) -> Seq Scan on ida_match_sources mtchsrc2 (cost=0.00..6.85 rows=185 width=8) (actual time=0.004..0.065 rows=185 loops=1) -> Hash (cost=22.58..22.58 rows=1 width=24) (actual time=0.162..0.162 rows=1 loops=1) -> Hash Join (cost=10.89..22.58 rows=1 width=24) (actual time=0.091..0.155 rows=1 loops=1) Hash Cond: (mtchsrcprj2.funding_source_id = mtchsrcprjfs2.nameid) -> Seq Scan on project mtchsrcprj2 (cost=0.00..11.22 rows=122 width=8) (actual time=0.005..0.060 rows=122 loops=1) -> Hash (cost=10.83..10.83 rows=5 width=24) (actual time=0.039..0.039 rows=1 loops=1) -> Index Scan using name_float_lfm_idx on namemaster mtchsrcprjfs2 (cost=0.00..10.83 rows=5 width=24) (actual time=0.028..0.030 rows=1 loops=1) Index Cond: (name_float_lfm = 'DWS'::text) -> Index Scan using accounts_pkey on accounts acc (cost=0.00..0.41 rows=1 width=12) (actual time=0.005..0.005 rows=1 loops=970) Index Cond: (acc.id = accmtchgrp.account_id) Filter: (program_id = 221) -> Index Scan using nameid_pk on namemaster dem (cost=0.00..3.02 rows=1 width=41) (actual time=0.006..0.007 rows=1 loops=970) Index Cond: (acc.owner_id = dem.nameid) Filter: (programid = 221) -> Index Scan using validanswerid_pk on validanswer accsts (cost=0.00..1.91 rows=1 width=21) (actual time=0.004..0.005 rows=0 loops=970) Index Cond: (acc.ida_account_status_id = accsts.validanswerid) Filter: (validvalue = 'Open'::text) -> Index Scan using ida_match_groups_pkey on ida_match_groups mtchgrp2 (cost=0.00..0.27 rows=1 width=4) (actual time=0.003..0.006 rows=1 loops=248) Index Cond: (accmtchgrp.match_group_id = mtchgrp2.id) -> GroupAggregate (cost=164.63..164.75 rows=1 width=129) (actual time=1.635..147.391 rows=230 loops=248) -> Sort (cost=164.63..164.64 rows=1 width=129) (actual time=1.407..3.160 rows=4715 loops=248) Sort Key: foo.ida_account_id, foo.ida_account_status, foo.ida_match_rate -> Sort (cost=164.61..164.61 rows=1 width=82) (actual time=340.444..341.726 rows=4715 loops=1) Sort Key: acc.id -> Nested Loop (cost=42.74..164.60 rows=1 width=82) (actual time=3.069..333.866 rows=4715 loops=1) -> Nested Loop (cost=42.74..164.29 rows=1 width=69) (actual time=3.062..310.340 rows=4715 loops=1) -> Nested Loop (cost=42.74..162.38 rows=1 width=56) (actual time=2.955..224.985 rows=20048 loops=1) - > Nested Loop (cost=42.74..162.09 rows=1 width=42) (actual time=2.947..135.616 rows=20048 loops=1) -> Nested Loop (cost=42.74..161.76 rows=1 width=38) (actual time=2.932..27.772 rows=20153 loops=1) -> Hash Join (cost=10.89..22.58 rows=1 width=24) (actual time=0.065..0.134 rows=1 loops=1) Hash Cond: (mtchsrcprj3.funding_source_id = mtchsrcprjfs3.nameid) -> Seq Scan on project mtchsrcprj3 (cost=0.00..11.22 rows=122 width=8) (actual time=0.002..0.054 rows=122 loops=1) -> Hash (cost=10.83..10.83 rows=5 width=24) (actual time=0.017..0.017 rows=1 loops=1) -> Index Scan using name_float_lfm_idx on namemaster mtchsrcprjfs3 (cost=0.00..10.83 rows=5 width=24) (actual time=0.012..0.013 rows=1 loops=1) Index Cond: (name_float_lfm = 'DWS'::text) -> Bitmap Heap Scan on transaction_details idatrndtl (cost=31.85..121.60 rows=1407 width=22) (actual time=2.864..12.060 rows=20153 loops=1) Recheck Cond: (idatrndtl.ida_trans_match_source_id = mtchsrcprj3.id) -> Bitmap Index Scan on transaction_details_ida_trans_match_source_id (cost=0.00..31.50 rows=1407 width=0) (actual time=2.696..2.696 rows=20153 loops=1) Index Cond: (idatrndtl.ida_trans_match_source_id = mtchsrcprj3.id) -> Index Scan using transactions_pkey on transactions idatrn (cost=0.00..0.31 rows=1 width=12) (actual time=0.003..0.004 rows=1 loops=20153) Index Cond: (idatrn.id = idatrndtl.transaction_id) Filter : (((transaction_date >= '2007-10-01'::date) OR (transaction_date <= '2007-10-01'::date)) AND (transaction_date <= '2007-12-31'::date)) - > Index Scan using accounts_pkey on accounts acc (cost=0.00..0.28 rows=1 width=18) (actual time=0.003..0.003 rows=1 loops=20048) Index Cond: (acc.id = idatrn.account_id) Filter : (program_id = 221) -> Index Scan using validanswerid_pk on validanswer accsts (cost=0.00..1.91 rows=1 width=21) (actual time=0.003..0.003 rows=0 loops=20048) Index Cond: (acc.ida_account_status_id = accsts.validanswerid) Filter: (validvalue = 'Open'::text) -> Index Scan using validanswerid_pk on validanswer trndtlcat (cost=0.00..0.29 rows=1 width=21) (actual time=0.003..0.004 rows=1 loops=4715) Index Cond: (idatrndtl.ida_trans_detail_category_id = trndtlcat.validanswerid) Filter: (validvalue = ANY ('{"Match Withdrawal","Match Earned","Match Interest"}'::text[])) -> Index Scan using validanswerid_pk on validanswer cou (cost=0.00..3.77 rows=1 width=21) (actual time=0.011..0.012 rows=1 loops=248) Index Cond: (cou.validanswerid = dem.county) Total runtime: 36622.135 ms (73 rows)
Chris Kratz <chris.kratz@vistashare.com> writes: > -> Nested Loop (cost=42.74..161.76 rows=1 width=38) (actual > time=2.932..27.772 rows=20153 loops=1) > -> Hash Join (cost=10.89..22.58 rows=1 width=24) (actual > time=0.065..0.134 rows=1 loops=1) > Hash Cond: (mtchsrcprj3.funding_source_id = > mtchsrcprjfs3.nameid) > -> Seq Scan on project mtchsrcprj3 (cost=0.00..11.22 > rows=122 width=8) (actual time=0.002..0.054 rows=122 loops=1) > -> Hash (cost=10.83..10.83 rows=5 width=24) (actual > time=0.017..0.017 rows=1 loops=1) > -> Index Scan using name_float_lfm_idx on > namemaster mtchsrcprjfs3 (cost=0.00..10.83 rows=5 width=24) (actual > time=0.012..0.013 rows=1 loops=1) > Index Cond: (name_float_lfm = 'DWS'::text) > -> Bitmap Heap Scan on transaction_details idatrndtl > (cost=31.85..121.60 rows=1407 width=22) (actual time=2.864..12.060 > rows=20153 loops=1) > Recheck Cond: (idatrndtl.ida_trans_match_source_id = > mtchsrcprj3.id) > -> Bitmap Index Scan on > transaction_details_ida_trans_match_source_id (cost=0.00..31.50 > rows=1407 width=0) (actual time=2.696..2.696 rows=20153 loops=1) > Index Cond: (idatrndtl.ida_trans_match_source_id = > mtchsrcprj3.id) > The first frustration is that I can't get the transaction details scan > to get any more accurate. It thinks it will find 1407 records, > instead it finds 20,153. Then for whatever reason it thinks that a > join between 1 record and 1407 records will return 1 record. This is > mainly what I can't understand. Why does it think it will only get > one record in response when it's a left join? I don't see any left join there ... > PG 8.2.4 on Linux kernel 2.6.9 x64 The first thing you should do is update to 8.2.6; we've fixed a fair number of problems since then that were fallout from the outer-join planning rewrite in 8.2. If it still doesn't work very well, please post the pg_stats rows for the join columns involved (idatrndtl.ida_trans_match_source_id and mtchsrcprj3.id). (You do have up-to-date ANALYZE stats for both of those tables, right?) regards, tom lane
On 2/11/08, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Chris Kratz <chris.kratz@vistashare.com> writes:
> -> Nested Loop (cost=42.74..161.76 rows=1 width=38) (actual
> time=2.932..27.772 rows=20153 loops=1)
> -> Hash Join (cost=10.89..22.58 rows=1 width=24) (actual
> time=0.065..0.134 rows=1 loops=1)
> Hash Cond: (mtchsrcprj3.funding_source_id =
> mtchsrcprjfs3.nameid)
> -> Seq Scan on project mtchsrcprj3 (cost=0.00..11.22
> rows=122 width=8) (actual time=0.002..0.054 rows=122 loops=1)
> -> Hash (cost=10.83..10.83 rows=5 width=24) (actual
> time=0.017..0.017 rows=1 loops=1)
> -> Index Scan using name_float_lfm_idx on
> namemaster mtchsrcprjfs3 (cost=0.00..10.83 rows=5 width=24) (actual
> time=0.012..0.013 rows=1 loops=1)
> Index Cond: (name_float_lfm = 'DWS'::text)
> -> Bitmap Heap Scan on transaction_details idatrndtl
> (cost=31.85..121.60 rows=1407 width=22) (actual time=2.864..12.060
> rows=20153 loops=1)
> Recheck Cond: (idatrndtl.ida_trans_match_source_id =
> mtchsrcprj3.id)
> -> Bitmap Index Scan on
> transaction_details_ida_trans_match_source_id (cost=0.00..31.50
> rows=1407 width=0) (actual time=2.696..2.696 rows=20153 loops=1)
> Index Cond: (idatrndtl.ida_trans_match_source_id =
> mtchsrcprj3.id)
> The first frustration is that I can't get the transaction details scan
> to get any more accurate. It thinks it will find 1407 records,
> instead it finds 20,153. Then for whatever reason it thinks that a
> join between 1 record and 1407 records will return 1 record. This is
> mainly what I can't understand. Why does it think it will only get
> one record in response when it's a left join?
I don't see any left join there ...
> PG 8.2.4 on Linux kernel 2.6.9 x64
The first thing you should do is update to 8.2.6; we've fixed a fair
number of problems since then that were fallout from the outer-join
planning rewrite in 8.2.
If it still doesn't work very well, please post the pg_stats rows for
the join columns involved (idatrndtl.ida_trans_match_source_id and
mtchsrcprj3.id). (You do have up-to-date ANALYZE stats for both
of those tables, right?)
regards, tom lane
Thanks Tom, we will try the upgrade and see if that makes a difference.
-Chris
On 2/11/08, Tom Lane <tgl@sss.pgh.pa.us> wrote:
This had no appreciable difference in the plan. Here is the part that seems to be causing the problem again after the increase in stats. It still thinks there is only one row in the result.
Chris Kratz <chris.kratz@vistashare.com> writes:
> -> Nested Loop (cost=42.74..161.76 rows=1 width=38) (actual
> time=2.932..27.772 rows=20153 loops=1)
> -> Hash Join (cost=10.89..22.58 rows=1 width=24) (actual
> time=0.065..0.134 rows=1 loops=1)
> Hash Cond: (mtchsrcprj3.funding_source_id =
> mtchsrcprjfs3.nameid)
> -> Seq Scan on project mtchsrcprj3 (cost=0.00..11.22
> rows=122 width=8) (actual time=0.002..0.054 rows=122 loops=1)
> -> Hash (cost=10.83..10.83 rows=5 width=24) (actual
> time=0.017..0.017 rows=1 loops=1)
> -> Index Scan using name_float_lfm_idx on
> namemaster mtchsrcprjfs3 (cost=0.00..10.83 rows=5 width=24) (actual
> time=0.012..0.013 rows=1 loops=1)
> Index Cond: (name_float_lfm = 'DWS'::text)
> -> Bitmap Heap Scan on transaction_details idatrndtl
> (cost=31.85..121.60 rows=1407 width=22) (actual time=2.864..12.060
> rows=20153 loops=1)
> Recheck Cond: (idatrndtl.ida_trans_match_source_id =
> mtchsrcprj3.id)
> -> Bitmap Index Scan on
> transaction_details_ida_trans_match_source_id (cost=0.00..31.50
> rows=1407 width=0) (actual time=2.696..2.696 rows=20153 loops=1)
> Index Cond: (idatrndtl.ida_trans_match_source_id =
> mtchsrcprj3.id)
> The first frustration is that I can't get the transaction details scan
> to get any more accurate. It thinks it will find 1407 records,
> instead it finds 20,153. Then for whatever reason it thinks that a
> join between 1 record and 1407 records will return 1 record. This is
> mainly what I can't understand. Why does it think it will only get
> one record in response when it's a left join?
I don't see any left join there ...
> PG 8.2.4 on Linux kernel 2.6.9 x64
The first thing you should do is update to 8.2.6; we've fixed a fair
number of problems since then that were fallout from the outer-join
planning rewrite in 8.2.
If it still doesn't work very well, please post the pg_stats rows for
the join columns involved (idatrndtl.ida_trans_match_source_id and
mtchsrcprj3.id). (You do have up-to-date ANALYZE stats for both
of those tables, right?)
regards, tom lane
I know it's somewhat premature as we haven't had a chance to do the update yet, but here is what I did w/ the statistics with the current version for chuckles and grins just to see if it would make a difference in the plan.
# alter table project alter column id set statistics 1000;
ALTER TABLE
# analyze project;
ANALYZE
# alter table transaction_details alter column ida_trans_match_source_id set statistics 1000;
ALTER TABLE
# analyze transaction_details;
ANALYZE
# select * from pg_stats where (tablename='project' and attname='id') or (tablename='transaction_details' and attname='ida_trans_match_source_id');
schemaname | tablename | attname | null_frac | avg_width | n_distinct | most_common_vals | most_common_freqs | histogram_bounds | correlation
------------+---------------------+---------------------------+-----------+-----------+------------+------------------------------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------
public | project | id | 0 | 4 | -1 | | | {6,7,8,12,13,14,15,17,18,19,24,25,26,27,28,29,30,31,32,33,34,35,36,37,41,42,71,72,797,802,803,809,812,813,814,815,816,817,818,822,823,824,825,826,827,828,829,830,831,832,833,834,835,836,837,838,839,840,841,842,843,844,845,846,847,848,849,920,921,922,923,924,925,926,927,928,929,930,931,932,933,934,935,936,937,938,939,940,941,942,946,947,948,949,950,951,952,953,954,955,956,957,958,959,960,961,962,963,964,965,966,967,968,969,970,971,972,973,974,975,977,978} | 0.939317
public | transaction_details | ida_trans_match_source_id | 0.480469 | 4 | 74 | {832,818,930,937,923,812,931,829,837,830,836,14,809,838,936,924,921,922,814,816,817,827,815,941,835,967,926,813,968,928,920,939,925,974,833,965,933} | {0.100562,0.100233,0.0412866,0.0245354,0.0223948,0.021277,0.0198998,0.018817,0.0182431,0.0181583,0.0180236,0.0141714,0.0107633,0.00955071,0.00917646,0.00639708,0.00562364,0.00491507,0.00453584,0.0037624,0.00332828,0.00332828,0.00323846,0.00309874,0.00295403,0.00267959,0.00234526,0.00227041,0.00221552,0.00220055,0.00215565,0.00207581,0.00179138,0.00136225,0.00114269,0.00113271,0.00100796} | {6,6,7,8,15,802,802,802,802,803,803,839,841,844,844,845,845,846,927,927,934,934,935,935,938,938,940,942,952,954,955,955,957,972,972,972,978} | 0.218267
(2 rows)
-> Nested Loop (cost=42.75..161.78 rows=1 width=38) (actual time=391.797..425.337 rows=20153 loops=1)
-> Hash Join (cost=10.89..22.58 rows=1 width=24) (actual time=0.069..0.139 rows=1 loops=1)
Hash Cond: (mtchsrcprj3.funding_source_id = mtchsrcprjfs3.nameid)
-> Seq Scan on project mtchsrcprj3 (cost=0.00..11.22 rows=122 width=8) (actual time=0.002..0.054 rows=122 loops=1)
-> Hash (cost=10.83..10.83 rows=5 width=24) (actual time=0.022..0.022 rows=1 loops=1)
-> Index Scan using name_float_lfm_idx on namemaster mtchsrcprjfs3 (cost=0.00..10.83 rows=5 width=24) (actual time=0.013..0.014 rows=1 loops=1)
Index Cond: (name_float_lfm = 'DWS'::text)
-> Bitmap Heap Scan on transaction_details idatrndtl (cost=31.87..121.61 rows=1407 width=22) (actual time=391.722..410.129 rows=20153 loops=1)
Recheck Cond: (idatrndtl.ida_trans_match_source_id = mtchsrcprj3.id)
-> Bitmap Index Scan on transaction_details_ida_trans_match_source_id (cost=0.00..31.51 rows=1407 width=0) (actual time=391.523..391.523 rows=20153 loops=1)
Index Cond: (idatrndtl.ida_trans_match_source_id = mtchsrcprj3.id)
Here is the relevant snippet from the query
<-- snip -->
FROM
accounts acc
left join transactions idatrn on (acc.id = idatrn.account_id)
left join transaction_details idatrndtl on (idatrn.id = idatrndtl.transaction_id)
left join project mtchsrcprj3 on (idatrndtl.ida_trans_match_source_id = mtchsrcprj3.id)
left join namemaster mtchsrcprjfs3 on ( mtchsrcprj3.funding_source_id = mtchsrcprjfs3.nameid)
<-- snip -->
I'll update again once we've had a chance to do the update.
-Chris
On 2/11/08, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Chris Kratz <chris.kratz@vistashare.com> writes:
> The first frustration is that I can't get the transaction details scan
> to get any more accurate. It thinks it will find 1407 records,
> instead it finds 20,153. Then for whatever reason it thinks that a
> join between 1 record and 1407 records will return 1 record. This is
> mainly what I can't understand. Why does it think it will only get
> one record in response when it's a left join?
I don't see any left join there ...
> PG 8.2.4 on Linux kernel 2.6.9 x64
The first thing you should do is update to 8.2.6; we've fixed a fair
number of problems since then that were fallout from the outer-join
planning rewrite in 8.2.
If it still doesn't work very well, please post the pg_stats rows for
the join columns involved (idatrndtl.ida_trans_match_source_id and
mtchsrcprj3.id). (You do have up-to-date ANALYZE stats for both
of those tables, right?)
regards, tom lane
Hello Tom,
We've updated to Postgres 8.2.6 on our production database over the weekend. Unfortunately, the estimates on this query are no better after the upgrade. Here is just the part of the estimate that is incorrect. (2 vs 20153)
-> Nested Loop (cost=12.68..165.69 rows=2 width=38) (actual time=0.089..29.792 rows=20153 loops=1)
-> Hash Join (cost=12.68..24.37 rows=1 width=24) (actual time=0.064..0.135 rows=1 loops=1)
Hash Cond: (mtchsrcprj3.funding_source_id = mtchsrcprjfs3.nameid)
-> Seq Scan on project mtchsrcprj3 (cost=0.00..11.22 rows=122 width=8) (actual time=0.002..0.053 rows=122 loops=1)
-> Hash (cost=12.61..12.61 rows=6 width=24) (actual time=0.017..0.017 rows=1 loops=1)
-> Index Scan using name_float_lfm_idx on namemaster mtchsrcprjfs3 (cost=0.00..12.61 rows=6 width=24) (actual time=0.012..0.013 rows=1 loops=1)
Index Cond: (name_float_lfm = 'DWS'::text)
-> Index Scan using transaction_details_ida_trans_match_source_id on transaction_details idatrndtl (cost=0.00..123.72 rows=1408 width=22) (actual time=0.023..17.128 rows=20153 loops=1)
(Entire explain analyze posted earlier in thread)
Total Query runtime: 35309.298 ms
Same w/ enable_nestloop off: 761.715 ms
I've tried the stats up to 1000 on both columns which causes no differences. Currently the stats are at 100.
test=# alter table transaction_details alter column ida_trans_match_source_id set statistics 100;
ALTER TABLE
test=# analyze transaction_details;
ANALYZE
test=# alter table project alter column id set statistics 100;
ALTER TABLE
test=# analyze project;
ANALYZE
Stats rows in pg_stats for these two columns:
test=# select * from pg_stats where tablename = 'transaction_details' and attname='ida_trans_match_source_id';
schemaname | tablename | attname | null_frac | avg_width | n_distinct | most_common_vals | most_common_freqs | histogram_bounds | correlation
------------+---------------------+---------------------------+-----------+-----------+------------+------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------
public | transaction_details | ida_trans_match_source_id | 0.479533 | 4 | 69 | {818,832,930,937,923,812,931,836,837,829,830,14,809} | {0.1024,0.0991333,0.0408,0.0232,0.0221,0.0219,0.0207,0.0188667,0.0186667,0.0177667,0.0176667,0.0130333,0.0118667} | {6,802,813,813,814,814,815,815,816,816,817,817,827,827,833,835,835,838,838,838,838,838,843,920,921,921,921,921,922,922,924,924,924,924,925,926,926,928,928,934,936,936,936,936,936,938,939,941,941,955,965,967,968,968,974,980} | 0.178655
(1 row)
test=# select * from pg_stats where tablename = 'project' and attname='id';
schemaname | tablename | attname | null_frac | avg_width | n_distinct | most_common_vals | most_common_freqs | histogram_bounds | correlation
------------+-----------+---------+-----------+-----------+------------+------------------+-------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------
public | project | id | 0 | 4 | -1 | | | {6,7,8,12,13,15,17,18,19,24,26,27,28,29,30,32,33,34,35,36,41,42,71,72,802,803,809,812,813,815,816,817,818,822,824,825,826,827,828,830,831,832,833,835,836,837,838,839,841,842,843,844,845,847,848,849,920,921,923,924,925,926,928,929,930,931,932,934,935,936,937,938,940,941,942,946,947,949,950,951,952,954,955,956,957,958,960,961,962,963,964,966,967,968,969,970,973,974,975,977,980} | 0.937228
(1 row)
PG 8.2.6 on linux x86_64, 8G ram, 4x15k->db, 2x10k-> OS & WAL
postgresql.conf settings of note:
shared_buffers = 1024MB
work_mem = 246MB
maintenance_work_mem = 256MB
random_page_cost = 1.75
effective_cache_size=2048MB
Any ideas how we can get the query to run faster?
Thanks,
-Chris
On 2/18/08, Chris Kratz <chris.kratz@vistashare.com> wrote:
Tom, any further ideas? I appreciate your help so far, but we are still stuck after the update to 8.2.6. Our only real solution at this point is to add code to our application that turns off nested loops for specific reports since the planner isn't getting correct estimates. I posted the pg_stat rows as requested above.On 2/11/08, Tom Lane <tgl@sss.pgh.pa.us> wrote:Chris Kratz <chris.kratz@vistashare.com> writes:
> The first frustration is that I can't get the transaction details scan
> to get any more accurate. It thinks it will find 1407 records,
> instead it finds 20,153. Then for whatever reason it thinks that a
> join between 1 record and 1407 records will return 1 record. This is
> mainly what I can't understand. Why does it think it will only get
> one record in response when it's a left join?
I don't see any left join there ...
> PG 8.2.4 on Linux kernel 2.6.9 x64
The first thing you should do is update to 8.2.6; we've fixed a fair
number of problems since then that were fallout from the outer-join
planning rewrite in 8.2.
If it still doesn't work very well, please post the pg_stats rows for
the join columns involved (idatrndtl.ida_trans_match_source_id and
mtchsrcprj3.id). (You do have up-to-date ANALYZE stats for both
of those tables, right?)
regards, tom laneHello Tom,
We've updated to Postgres 8.2.6 on our production database over the weekend. Unfortunately, the estimates on this query are no better after the upgrade. Here is just the part of the estimate that is incorrect. (2 vs 20153)
-> Nested Loop (cost=12.68..165.69 rows=2 width=38) (actual time=0.089..29.792 rows=20153 loops=1)-> Hash Join (cost=12.68..24.37 rows=1 width=24) (actual time=0.064..0.135 rows=1 loops=1)Hash Cond: (mtchsrcprj3.funding_source_id = mtchsrcprjfs3.nameid)-> Seq Scan on project mtchsrcprj3 (cost=0.00..11.22 rows=122 width=8) (actual time=0.002..0.053 rows=122 loops=1)-> Hash (cost=12.61..12.61 rows=6 width=24) (actual time=0.017..0.017 rows=1 loops=1)-> Index Scan using name_float_lfm_idx on namemaster mtchsrcprjfs3 (cost=0.00..12.61 rows=6 width=24) (actual time=0.012..0.013 rows=1 loops=1)Index Cond: (name_float_lfm = 'DWS'::text)-> Index Scan using transaction_details_ida_trans_match_source_id on transaction_details idatrndtl (cost=0.00..123.72 rows=1408 width=22) (actual time=0.023..17.128 rows=20153 loops=1)
(Entire explain analyze posted earlier in thread)
Total Query runtime: 35309.298 msSame w/ enable_nestloop off: 761.715 ms
I've tried the stats up to 1000 on both columns which causes no differences. Currently the stats are at 100.
test=# alter table transaction_details alter column ida_trans_match_source_id set statistics 100;ALTER TABLEtest=# analyze transaction_details;ANALYZEtest=# alter table project alter column id set statistics 100;ALTER TABLEtest=# analyze project;ANALYZE
Stats rows in pg_stats for these two columns:
test=# select * from pg_stats where tablename = 'transaction_details' and attname='ida_trans_match_source_id';schemaname | tablename | attname | null_frac | avg_width | n_distinct | most_common_vals | most_common_freqs | histogram_bounds | correlation------------+---------------------+---------------------------+-----------+-----------+------------+------------------------------------------------------+-------------------------------------------------------------------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------public | transaction_details | ida_trans_match_source_id | 0.479533 | 4 | 69 | {818,832,930,937,923,812,931,836,837,829,830,14,809} | {0.1024,0.0991333,0.0408,0.0232,0.0221,0.0219,0.0207,0.0188667,0.0186667,0.0177667,0.0176667,0.0130333,0.0118667} | {6,802,813,813,814,814,815,815,816,816,817,817,827,827,833,835,835,838,838,838,838,838,843,920,921,921,921,921,922,922,924,924,924,924,925,926,926,928,928,934,936,936,936,936,936,938,939,941,941,955,965,967,968,968,974,980} | 0.178655(1 row)
test=# select * from pg_stats where tablename = 'project' and attname='id';schemaname | tablename | attname | null_frac | avg_width | n_distinct | most_common_vals | most_common_freqs | histogram_bounds | correlation------------+-----------+---------+-----------+-----------+------------+------------------+-------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-------------public | project | id | 0 | 4 | -1 | | | {6,7,8,12,13,15,17,18,19,24,26,27,28,29,30,32,33,34,35,36,41,42,71,72,802,803,809,812,813,815,816,817,818,822,824,825,826,827,828,830,831,832,833,835,836,837,838,839,841,842,843,844,845,847,848,849,920,921,923,924,925,926,928,929,930,931,932,934,935,936,937,938,940,941,942,946,947,949,950,951,952,954,955,956,957,958,960,961,962,963,964,966,967,968,969,970,973,974,975,977,980} | 0.937228(1 row)
PG 8.2.6 on linux x86_64, 8G ram, 4x15k->db, 2x10k-> OS & WAL
postgresql.conf settings of note:
shared_buffers = 1024MBwork_mem = 246MBmaintenance_work_mem = 256MBrandom_page_cost = 1.75effective_cache_size=2048MB
Any ideas how we can get the query to run faster?
Thanks,
-Chris
Thanks,
-Chris