Postgres how to calculate work_mem

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set work_mem='1MB'; select ...; // running time is ~1800 ms set work_mem='96MB'; select ...' // running time is ~1500 ms When I do exactly the same query (the one above) with exactly the same data on the server I get 2100 ms with work_mem=1MB and 3200 ms with 96 MB. Other factors may be DB page size/amount, how fragmented that data is, work_mem settings, etc. – geozelot Mar 11 at 13:30 @Pin_Eipol updated the methodology to use the mighty <-> operator for (K) Nearest Neighbor searches; I haven't had the time to write this up yesterday. – geozelot Mar 11 at 14:29 This parameter has no effect on the size of shared memory allocated by PostgreSQL, nor does it reserve kernel disk cache; it is used only for estimation purposes. The default is 128 megabytes (128MB). work_mem (integer) Specifies the amount of memory to be used by internal sort operations and hash tables before switching to temporary disk files ... I noticed that when I increase max_connections, the recommended work_mem decreases. PGTune assumes that if more connections are open, then there will be more queries running simultaneously, and then more multiple of work_mem are likely to be allocated, but such allocations happen on the fly. Oct 14, 2020 · work_mem. If you do a lot of complex sorts, and have a lot of memory, then increasing the work_mem parameter allows PostgreSQL to do larger in-memory sorts which, unsurprisingly, will be faster than disk-based equivalents. This size is applied to each and every sort done by each user, and complex queries can use multiple working memory sort ... PostgreSQL Common Utility Queries. GitHub Gist: instantly share code, notes, and snippets. r/PostgreSQL: The home of the most advanced Open Source database server on the worlds largest and most active Front Page of the Internet. Press J to jump to the feed. Press question mark to learn the rest of the keyboard shortcuts my postgres server isn’t entirely dedicated to executing this one example sql statement and nothing else. by increasing the value of work_mem , i’ve increased it server-wide for every request ... set work_mem='1MB'; select ...; // running time is ~1800 ms set work_mem='96MB'; select ...' // running time is ~1500 ms When I do exactly the same query (the one above) with exactly the same data on the server I get 2100 ms with work_mem=1MB and 3200 ms with 96 MB. Regardless of how much memory my server hardware actually has, Postgres won’t allow the hash table to consume more than 4MB. This value is the work_mem setting found in the postgresql.conf file. At the same time Postgres calculates the number of buckets, it also calculates the total amount of memory it expects the hash table to consume. Mar 05, 2012 · trying to understand how much memory postgres could use, and how to change the configuration to bring it down to a level that won't get it killed. Key configuration values are: max_connections = 350 shared_buffers = 4GB temp_buffers = 24MB max_prepared_transactions = 211 work_mem = 16MB maintenance_work_mem = 131MB wal_buffers = -1 wal_keep ... Aug 24, 2016 · work_mem. work_mem is the amount of memory allocated to each Postgres operation (see max_connections) This determines how much memory a single Postgres operation can use, and is especially helpful for complex sorts and joins. Jan 19, 2018 · To learn how to calculate linear correlation between multiple columns, see: Use PostgreSQL to calculate the linear correlation between fields of any type. Data distribution has another benefit in that it significantly increases the compression ratio for column storage. You can calculate how many dead tuples vacuum can process in a single pass by dividing maintenance_work_mem (in bytes) by 6. Setting the autovacuum_work_mem or maintenance_work_mem parameters sets the maximum memory size that each autovacuum worker process should use the 16M work mem * 600 has to do with the fact that if you had 600 clients connected, and they all ran a query with 1 sort (a query can have > 1 sort by the way) then it would require 600*sort_mem (now work_mem) memory for the server to handle all these sorts, on top of the memory being used for other things. I created a “base time” to calculate this efficiency by simply disabling parallelism altogether, and running the query on a single CPU core, which resulted in a query time of 9052.8 seconds. The fastest times I saw were around the 72 to 76 parallel worker mark, with 149.7 and 148.6 seconds respectively. May 05, 2020 · PGTune is used to calculate configuration parameters for PostgreSQL based on the maximum performance for a given hardware configuration. It isn't a silver bullet though, as many settings depend not only on the hardware configuration, but also on the size of the database, the number of clients and the complexity of queries. PostgreSQL: Improve the performance of Query Sort operation by setting work_mem PostgreSQL: How to Disable or Enable Foreign Key Constraint of a Table PostgreSQL: How to find last Day of the Month Oct 14, 2020 · work_mem. If you do a lot of complex sorts, and have a lot of memory, then increasing the work_mem parameter allows PostgreSQL to do larger in-memory sorts which, unsurprisingly, will be faster than disk-based equivalents. This size is applied to each and every sort done by each user, and complex queries can use multiple working memory sort ... r/PostgreSQL: The home of the most advanced Open Source database server on the worlds largest and most active Front Page of the Internet. Press J to jump to the feed. Press question mark to learn the rest of the keyboard shortcuts 2- The work_mem can be calculate on base of connections and memory(RAM), but the work_mem needs to change something if I enable the parallel? My supposition is: if the machine has 8 cores the max_parallel_workers is 8 and the values of worker process and per gather are 32(8*4), the number 4 I took from the original configuration that is 4 ... I created a “base time” to calculate this efficiency by simply disabling parallelism altogether, and running the query on a single CPU core, which resulted in a query time of 9052.8 seconds. The fastest times I saw were around the 72 to 76 parallel worker mark, with 149.7 and 148.6 seconds respectively. the 16M work mem * 600 has to do with the fact that if you had 600 clients connected, and they all ran a query with 1 sort (a query can have > 1 sort by the way) then it would require 600*sort_mem (now work_mem) memory for the server to handle all these sorts, on top of the memory being used for other things. Apr 16, 2016 · SET work_mem = '256MB'; SELECT * FROM users ORDER BY LOWER(display_name); RESET work_mem; This example sets work_mem for a single transaction and then automatically resets it to the server default value. SET LOCAL work_mem = '256MB'; SELECT * FROM users ORDER BY LOWER(display_name); You can learn more about SET command in PostgreSQL documentation. work_mem (integer) Specifies the amount of memory to be used by internal sort operations and hash tables before writing to temporary disk files. The value defaults to four megabytes (4MB). Note that for a complex query, several sort or hash operations might be running in parallel; each operation will be allowed to use as much memory as this ... Regardless of how much memory my server hardware actually has, Postgres won’t allow the hash table to consume more than 4MB. This value is the work_mem setting found in the postgresql.conf file. At the same time Postgres calculates the number of buckets, it also calculates the total amount of memory it expects the hash table to consume. See full list on wiki.postgresql.org Sep 12, 2014 · The following tutorial will list some simple commands to help you find or calculate the disk usage of several PostgreSQL objects. This includes tables, indexes, views, tablespaces, and so on. For the following examples I used the PostgreSQL 9.3.2 See full list on datadoghq.com r/PostgreSQL: The home of the most advanced Open Source database server on the worlds largest and most active Front Page of the Internet. Press J to jump to the feed. Press question mark to learn the rest of the keyboard shortcuts See full list on datadoghq.com May 05, 2020 · PGTune is used to calculate configuration parameters for PostgreSQL based on the maximum performance for a given hardware configuration. It isn't a silver bullet though, as many settings depend not only on the hardware configuration, but also on the size of the database, the number of clients and the complexity of queries.