Index Only ScanĪ scan on an index that did not require fetching anything from the table. Retrieving lots of rows, so it’s best to avoid these for large tables. This is like usingĪrray#each, but on a database table. Seq ScanĪ sequential scan over (a chunk of) a database table. PgMustard’s EXPLAIN docs also offer detailed look into nodes and their fields. There are quite a few different types of nodes, so we only cover some of theĪ full list of all the available nodes and their descriptions can be found in Here we can see that this node used 3552 buffers (3543 + 9), returned 888 rows ( 888 * 1), and the actual duration was 22.2 milliseconds ( 888 * 0.025).ġ7.76 milliseconds of the total duration was spent in reading from disk, to retrieve data that was not in the cache. ![]() author_id ) Buffers : shared hit = 3543 read = 9 I / O Timings : read = 17. 025 rows = 1 loops = 888 ) Index Cond : ( users. 44 rows = 1 width = 1318 ) ( actual time = 0. > Index Scan using users_pkey on public. Number of rows produced, the number of loops performed, and more. Node statisticsĮach node in a plan has a set of associated statistics, such as the cost, the “Nested Loop” on the result of these two scans. Here we first perform two separate “Index Only” scans, followed by performing a ![]() 003 rows = 1 loops = 36 ) Index Cond : ( id = users_1. 96 rows = 1 width = 4 ) ( actual time = 0. 123 rows = 36 loops = 1 ) Index Cond : ( id Index Only Scan using users_pkey on users ( cost = 0. 95 rows = 87 width = 4 ) ( actual time = 0. 249 rows = 36 loops = 1 ) Buffers : shared hit = 155 -> Index Only Scan using users_pkey on users users_1 ( cost = 0. 75 rows = 87 width = 0 ) ( actual time = 0. 252 rows = 1 loops = 1 ) Buffers : shared hit = 155 -> Nested Loop ( cost = 0. 98 rows = 1 width = 8 ) ( actual time = 0.
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