如何优化两个索引列上的 PostgreSQL OR 查询

Question

如何优化两个索引列上的 PostgreSQL OR 查询

nic*_*314 5 postgresql index execution-plan index-tuning query-performance

我有一个大型分区表，用于存储帐户之间的货币交易。

CREATE TABLE "transactions" (
  "from" BYTEA        NOT NULL  -- sender account
  ,"to" BYTEA         NOT NULL  -- receiver account
  ,"type" INTEGER     NOT NULL  -- type of transfer
  ,"ts" TIMESTAMP     NOT NULL  -- timestamp of transfer
) PARTITION BY RANGE ("ts");

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“transactions”在“ts”、“from”和“to”上有索引（“ts”用于排序）。

CREATE INDEX "transactions_ts_idx"   ON "transactions" USING BTREE ("ts");
CREATE INDEX "transactions_from_idx" ON "transactions" USING BTREE ("from", "ts");
CREATE INDEX "transactions_to_idx"   ON "transactions" USING BTREE ("to",   "ts");

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我想查询涉及给定帐户或没有帐户的所有交易，例如：

-- given an account <account>
SELECT * FROM "transactions"
WHERE "from" = '<account>' OR "to" = '<account>'
ORDER BY "ts" DESC;

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和

-- all transactions irrespective of account
SELECT * FROM "transactions"
ORDER BY "ts" DESC;

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SELECT * FROM "transactions"
WHERE "from" = '<account>' OR "to" = '<account>'
ORDER BY "ts" DESC;

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正如预期的那样，给定的第一个查询的后续查询计划<account>涉及对“from”和“to”索引进行 BITMAP INDEX SCAN，然后在每个分区上进行 BITMAP OR。

...
|  ->  BitmapOr  (cost=535.22..535.22 rows=17744 width=0) (actual time=6.355..6.356 rows=0 loops=1)                                     |
|    ->  Bitmap Index Scan on transactions_2022_12_from_idx  (cost=0.00..185.51 rows=7058 width=0) (actual time=2.742..2.742 rows=0 loops=1)  |
|      Index Cond: (("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                            |
|    ->  Bitmap Index Scan on transactions_2022_12_to_idx  (cost=0.00..340.84 rows=10686 width=0) (actual time=3.613..3.613 rows=0 loops=1)     |
|      Index Cond: (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                              |
...

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然而，考虑到该查询计划的频率，我担心它的 CPU 和内存。

是否有其他方法来构造表或索引以使查询更有效？

例如，表可以从单条目切换到双条目结构，其中表中的每一行变成三行，并带有新列“account”（“from”、“to”或 null 用于查询，无论“account”如何）、“对手方”（“to”、“from”或 null ->“账户”的对手方）和“角色”（“sender”、“receiver”或 null）而不是“from”和“to” ”。

编辑

响应@a_horse_with_no_name，这里是完整的查询计划

...
|  ->  BitmapOr  (cost=535.22..535.22 rows=17744 width=0) (actual time=6.355..6.356 rows=0 loops=1)                                     |
|    ->  Bitmap Index Scan on transactions_2022_12_from_idx  (cost=0.00..185.51 rows=7058 width=0) (actual time=2.742..2.742 rows=0 loops=1)  |
|      Index Cond: (("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                            |
|    ->  Bitmap Index Scan on transactions_2022_12_to_idx  (cost=0.00..340.84 rows=10686 width=0) (actual time=3.613..3.613 rows=0 loops=1)     |
|      Index Cond: (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                              |
...

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+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| QUERY PLAN                                                                                                                                                                             |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Limit  (cost=306390.44..306390.46 rows=10 width=55) (actual time=0.268..0.272 rows=10 loops=1)                                                                                         |
|   ->  Sort  (cost=306390.44..306585.11 rows=77870 width=55) (actual time=0.267..0.270 rows=10 loops=1)                                                                                 |
|         Sort Key: transactions.ts DESC                                                                                                                                                 |
|         Sort Method: top-N heapsort  Memory: 27kB                                                                                                                                      |
|         ->  Append  (cost=50.80..304707.70 rows=77870 width=55) (actual time=0.099..0.241 rows=120 loops=1)                                                                            |
|               ->  Bitmap Heap Scan on transactions_2022_04 transactions_1  (cost=50.80..6666.09 rows=1709 width=58) (actual time=0.041..0.041 rows=0 loops=1)                          |
|                     Recheck Cond: ((("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea) OR (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea))   |
|                     ->  BitmapOr  (cost=50.80..50.80 rows=1709 width=0) (actual time=0.039..0.040 rows=0 loops=1)                                                                      |
|                           ->  Bitmap Index Scan on transactions_2022_04_from_ts_idx  (cost=0.00..23.55 rows=932 width=0) (actual time=0.034..0.034 rows=0 loops=1)                     |
|                                 Index Cond: (("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                    |
|                           ->  Bitmap Index Scan on transactions_2022_04_to_ts_idx  (cost=0.00..26.39 rows=777 width=0) (actual time=0.005..0.005 rows=0 loops=1)                       |
|                                 Index Cond: (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                      |
|               ->  Bitmap Heap Scan on transactions_2022_05 transactions_2  (cost=535.22..69369.48 rows=17744 width=56) (actual time=0.011..0.012 rows=0 loops=1)                       |
|                     Recheck Cond: ((("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea) OR (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea))   |
|                     ->  BitmapOr  (cost=535.22..535.22 rows=17744 width=0) (actual time=0.011..0.011 rows=0 loops=1)                                                                   |
|                           ->  Bitmap Index Scan on transactions_2022_05_from_ts_idx  (cost=0.00..185.51 rows=7058 width=0) (actual time=0.005..0.005 rows=0 loops=1)                   |
|                                 Index Cond: (("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                    |
|                           ->  Bitmap Index Scan on transactions_2022_05_to_ts_idx  (cost=0.00..340.84 rows=10686 width=0) (actual time=0.006..0.006 rows=0 loops=1)                    |
|                                 Index Cond: (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                      |
|               ->  Bitmap Heap Scan on transactions_2022_06 transactions_3  (cost=389.80..48846.95 rows=12582 width=54) (actual time=0.011..0.011 rows=0 loops=1)                       |
|                     Recheck Cond: ((("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea) OR (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea))   |
|                     ->  BitmapOr  (cost=389.80..389.80 rows=12582 width=0) (actual time=0.011..0.011 rows=0 loops=1)                                                                   |
|                           ->  Bitmap Index Scan on transactions_2022_06_from_ts_idx  (cost=0.00..127.32 rows=4634 width=0) (actual time=0.006..0.006 rows=0 loops=1)                   |
|                                 Index Cond: (("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                    |
|                           ->  Bitmap Index Scan on transactions_2022_06_to_ts_idx  (cost=0.00..256.19 rows=7949 width=0) (actual time=0.005..0.005 rows=0 loops=1)                     |
|                                 Index Cond: (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                      |
|               ->  Bitmap Heap Scan on transactions_2022_07 transactions_4  (cost=469.78..58879.05 rows=15080 width=55) (actual time=0.010..0.010 rows=0 loops=1)                       |
|                     Recheck Cond: ((("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea) OR (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea))   |
|                     ->  BitmapOr  (cost=469.78..469.78 rows=15080 width=0) (actual time=0.010..0.010 rows=0 loops=1)                                                                   |
|                           ->  Bitmap Index Scan on transactions_2022_07_from_ts_idx  (cost=0.00..142.28 rows=5028 width=0) (actual time=0.005..0.005 rows=0 loops=1)                   |
|                                 Index Cond: (("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                    |
|                           ->  Bitmap Index Scan on transactions_2022_07_to_ts_idx  (cost=0.00..319.96 rows=10052 width=0) (actual time=0.005..0.005 rows=0 loops=1)                    |
|                                 Index Cond: (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                      |
|               ->  Bitmap Heap Scan on transactions_2022_08 transactions_5  (cost=269.33..33314.79 rows=8524 width=55) (actual time=0.025..0.077 rows=77 loops=1)                       |
|                     Recheck Cond: ((("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea) OR (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea))   |
|                     Heap Blocks: exact=65                                                                                                                                              |
|                     ->  BitmapOr  (cost=269.33..269.33 rows=8524 width=0) (actual time=0.017..0.017 rows=0 loops=1)                                                                    |
|                           ->  Bitmap Index Scan on transactions_2022_08_from_ts_idx  (cost=0.00..81.88 rows=2841 width=0) (actual time=0.010..0.010 rows=64 loops=1)                   |
|                                 Index Cond: (("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                    |
|                           ->  Bitmap Index Scan on transactions_2022_08_to_ts_idx  (cost=0.00..183.19 rows=5683 width=0) (actual time=0.007..0.007 rows=30 loops=1)                    |
|                                 Index Cond: (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                      |
|               ->  Bitmap Heap Scan on transactions_2022_09 transactions_6  (cost=247.75..30679.40 rows=7826 width=55) (actual time=0.015..0.030 rows=21 loops=1)                       |
|                     Recheck Cond: ((("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea) OR (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea))   |
|                     Heap Blocks: exact=20                                                                                                                                              |
|                     ->  BitmapOr  (cost=247.75..247.75 rows=7826 width=0) (actual time=0.013..0.013 rows=0 loops=1)                                                                    |
|                           ->  Bitmap Index Scan on transactions_2022_09_from_ts_idx  (cost=0.00..76.60 rows=2671 width=0) (actual time=0.007..0.007 rows=19 loops=1)                   |
|                                 Index Cond: (("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                    |
|                           ->  Bitmap Index Scan on transactions_2022_09_to_ts_idx  (cost=0.00..167.23 rows=5155 width=0) (actual time=0.005..0.005 rows=4 loops=1)                     |
|                                 Index Cond: (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                      |
|               ->  Bitmap Heap Scan on transactions_2022_10 transactions_7  (cost=215.28..26566.61 rows=6767 width=55) (actual time=0.016..0.030 rows=21 loops=1)                       |
|                     Recheck Cond: ((("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea) OR (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea))   |
|                     Heap Blocks: exact=20                                                                                                                                              |
|                     ->  BitmapOr  (cost=215.28..215.28 rows=6767 width=0) (actual time=0.013..0.013 rows=0 loops=1)                                                                    |
|                           ->  Bitmap Index Scan on transactions_2022_10_from_ts_idx  (cost=0.00..59.88 rows=2041 width=0) (actual time=0.007..0.008 rows=19 loops=1)                   |
|                                 Index Cond: (("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                    |
|                           ->  Bitmap Index Scan on transactions_2022_10_to_ts_idx  (cost=0.00..152.01 rows=4726 width=0) (actual time=0.006..0.006 rows=5 loops=1)                     |
|                                 Index Cond: (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                      |
|               ->  Bitmap Heap Scan on transactions_2022_11 transactions_8  (cost=213.57..25724.08 rows=6554 width=55) (actual time=0.011..0.012 rows=1 loops=1)                        |
|                     Recheck Cond: ((("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea) OR (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea))   |
|                     Heap Blocks: exact=1                                                                                                                                               |
|                     ->  BitmapOr  (cost=213.57..213.57 rows=6554 width=0) (actual time=0.010..0.010 rows=0 loops=1)                                                                    |
|                           ->  Bitmap Index Scan on transactions_2022_11_from_ts_idx  (cost=0.00..53.07 rows=1667 width=0) (actual time=0.006..0.006 rows=1 loops=1)                    |
|                                 Index Cond: (("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                    |
|                           ->  Bitmap Index Scan on transactions_2022_11_to_ts_idx  (cost=0.00..157.22 rows=4887 width=0) (actual time=0.004..0.004 rows=0 loops=1)                     |
|                                 Index Cond: (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                      |
|               ->  Bitmap Heap Scan on transactions_2022_12 transactions_9  (cost=57.80..4271.89 rows=1084 width=55) (actual time=0.009..0.009 rows=0 loops=1)                          |
|                     Recheck Cond: ((("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea) OR (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea))   |
|                     ->  BitmapOr  (cost=57.80..57.80 rows=1084 width=0) (actual time=0.008..0.009 rows=0 loops=1)                                                                      |
|                           ->  Bitmap Index Scan on transactions_2022_12_from_ts_idx  (cost=0.00..14.46 rows=253 width=0) (actual time=0.004..0.004 rows=0 loops=1)                     |
|                                 Index Cond: (("from")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                    |
|                           ->  Bitmap Index Scan on transactions_2022_12_to_ts_idx  (cost=0.00..42.80 rows=831 width=0) (actual time=0.004..0.004 rows=0 loops=1)                       |
|                                 Index Cond: (("to")::bytea = '\xc5db3df907e7aa97f2da491e328578be27e9e644'::bytea)                                                                      |
| Planning Time: 0.410 ms                                                                                                                                                                |
| Execution Time: 0.334 ms                                                                                                                                                               |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
EXPLAIN 74

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Answer 1

Lau*_*lbe 9

该查询不会变得更快。请注意，您将无法同时支持WHERE条件索引和ORDER BYwith 索引；你必须决定你想要哪一个。为了支持该条件，请在和WHERE上建立索引；为了支持，有一个索引。fromtoORDER BYts

如果您愿意重写查询，它可能会更快：

((SELECT ts, "from", "to", value
  FROM transactions
  WHERE "from" = '\xc5db3df907e7aa97f2da491e328578be27e9e644'
  ORDER BY ts DESC
  LIMIT 10)
 UNION ALL
 (SELECT ts, "from", "to", value
  FROM transactions
  WHERE "to" = '\xc5db3df907e7aa97f2da491e328578be27e9e644'
  ORDER BY ts DESC
  LIMIT 10))
ORDER BY ts DESC
LIMIT 10;

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该查询将受益于两个索引，一个在上("from", ts)，一个在上("to", ts)。

您应该避免使用 SQL 关键字的列名。

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