{"id":11011,"date":"2018-03-09T06:25:04","date_gmt":"2018-03-09T05:25:04","guid":{"rendered":"https:\/\/www.dbi-services.com\/blog\/parallel-pg_dump-is-slow-by-default\/"},"modified":"2018-03-09T06:25:04","modified_gmt":"2018-03-09T05:25:04","slug":"parallel-pg_dump-is-slow-by-default","status":"publish","type":"post","link":"https:\/\/www.dbi-services.com\/blog\/parallel-pg_dump-is-slow-by-default\/","title":{"rendered":"Parallel pg_dump is slow by default?"},"content":{"rendered":"<p>Short answer: Yes, it is. Being at a customer the last days we wanted to parallel pg_dump a 2TB database. We were quite surprised that it was quite slow and it was not immediately clear why it was. Well, the answer is in the <a href=\"https:\/\/www.postgresql.org\/docs\/10\/static\/app-pgdump.html\" target=\"_blank\" rel=\"noopener\">documentation<\/a>: When you go for parallel dumps you need to use the directory format and this comes with: &#8220;This format is compressed by default and also supports parallel dumps.&#8221;. Compression takes time, so the question was if we could disable compression which was not clear from the statement: Does &#8220;compressed by default&#8221; mean that it per default is compressed and you can not change that or does it just mean it is the default, but you can change it?<\/p>\n<p><!--more--><\/p>\n<p>As always, lets setup a short test case:<\/p>\n<pre class=\"brush: sql; gutter: true; first-line: 1\">\npostgres=# create table dmp1 as \n           select a,a::varchar b,now() c \n             from generate_series ( 1, 1000000) a;\nSELECT 1000000\npostgres=# create table dmp2 as select * from dmp1;\nSELECT 1000000\npostgres=# create table dmp3 as select * from dmp1;\nSELECT 1000000\npostgres=# create table dmp4 as select * from dmp1;\nSELECT 1000000\npostgres=# d dmp*\n                        Table \"public.dmp1\"\n Column |           Type           | Collation | Nullable | Default \n--------+--------------------------+-----------+----------+---------\n a      | integer                  |           |          | \n b      | character varying        |           |          | \n c      | timestamp with time zone |           |          | \n\n                        Table \"public.dmp2\"\n Column |           Type           | Collation | Nullable | Default \n--------+--------------------------+-----------+----------+---------\n a      | integer                  |           |          | \n b      | character varying        |           |          | \n c      | timestamp with time zone |           |          | \n\n                        Table \"public.dmp3\"\n Column |           Type           | Collation | Nullable | Default \n--------+--------------------------+-----------+----------+---------\n a      | integer                  |           |          | \n b      | character varying        |           |          | \n c      | timestamp with time zone |           |          | \n\n                        Table \"public.dmp4\"\n Column |           Type           | Collation | Nullable | Default \n--------+--------------------------+-----------+----------+---------\n a      | integer                  |           |          | \n b      | character varying        |           |          | \n c      | timestamp with time zone |           |          | \n\n<\/pre>\n<p>We have four tables each containing 1&#8217;000&#8217;000 rows. When we use pg_dump in parallel with the default it looks like this:<\/p>\n<pre class=\"brush: bash; gutter: true; first-line: 1\">\npostgres@pgbox:\/home\/postgres\/ [PG10] mkdir \/var\/tmp\/dmp\npostgres@pgbox:\/home\/postgres\/ [PG10] time pg_dump --format=d --jobs=4 --file=\/var\/tmp\/dmp\/ postgres\n\nreal\t0m2.788s\nuser\t0m2.459s\nsys\t0m0.597s\npostgres@pgbox:\/home\/postgres\/ [PG10] ls -la \/var\/tmp\/dmp\/\ntotal 19528\ndrwxr-xr-x. 2 postgres postgres    4096 Mar  9 07:16 .\ndrwxrwxrwt. 4 root     root          51 Mar  9 07:15 ..\n-rw-r--r--. 1 postgres postgres      25 Mar  9 07:16 3113.dat.gz\n-rw-r--r--. 1 postgres postgres      25 Mar  9 07:16 3114.dat.gz\n-rw-r--r--. 1 postgres postgres      25 Mar  9 07:16 3115.dat.gz\n-rw-r--r--. 1 postgres postgres 4991138 Mar  9 07:16 3116.dat.gz\n-rw-r--r--. 1 postgres postgres 4991138 Mar  9 07:16 3117.dat.gz\n-rw-r--r--. 1 postgres postgres 4991138 Mar  9 07:16 3118.dat.gz\n-rw-r--r--. 1 postgres postgres 4991138 Mar  9 07:16 3119.dat.gz\n-rw-r--r--. 1 postgres postgres    5819 Mar  9 07:16 toc.dat\n<\/pre>\n<p>As stated in the documentation the result is compressed. When speed is more important then the size on disk you can however disable the compression:<\/p>\n<pre class=\"brush: bash; gutter: true; first-line: 1\">\npostgres@pgbox:\/home\/postgres\/ [PG10] rm -rf \/var\/tmp\/dmp\/*\npostgres@pgbox:\/home\/postgres\/ [PG10] time pg_dump --format=d --jobs=4 --file=\/var\/tmp\/dmp\/ --compress=0 postgres\n\nreal\t0m5.357s\nuser\t0m0.065s\nsys\t0m0.460s\npostgres@pgbox:\/home\/postgres\/ [PG10] ls -la \/var\/tmp\/dmp\/\ntotal 171040\ndrwxr-xr-x. 2 postgres postgres     4096 Mar  9 07:18 .\ndrwxrwxrwt. 4 root     root           51 Mar  9 07:15 ..\n-rw-r--r--. 1 postgres postgres        5 Mar  9 07:18 3113.dat\n-rw-r--r--. 1 postgres postgres        5 Mar  9 07:18 3114.dat\n-rw-r--r--. 1 postgres postgres        5 Mar  9 07:18 3115.dat\n-rw-r--r--. 1 postgres postgres 43777797 Mar  9 07:18 3116.dat\n-rw-r--r--. 1 postgres postgres 43777797 Mar  9 07:18 3117.dat\n-rw-r--r--. 1 postgres postgres 43777797 Mar  9 07:18 3118.dat\n-rw-r--r--. 1 postgres postgres 43777797 Mar  9 07:18 3119.dat\n-rw-r--r--. 1 postgres postgres     5819 Mar  9 07:18 toc.dat\n<\/pre>\n<p>In my case it got slower than the compressed dump but this is because I do not really have fast disks on my little VM. When you have a good storage solution disabling compression should bring you more speed.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Short answer: Yes, it is. Being at a customer the last days we wanted to parallel pg_dump a 2TB database. We were quite surprised that it was quite slow and it was not immediately clear why it was. Well, the answer is in the documentation: When you go for parallel dumps you need to use [&hellip;]<\/p>\n","protected":false},"author":28,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[229],"tags":[77],"type_dbi":[],"class_list":["post-11011","post","type-post","status-publish","format-standard","hentry","category-database-administration-monitoring","tag-postgresql"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v28.8 (Yoast SEO v28.8) - https:\/\/yoast.com\/product\/yoast-seo-premium-wordpress\/ -->\n<title>Parallel pg_dump is slow by default? - dbi Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.dbi-services.com\/blog\/parallel-pg_dump-is-slow-by-default\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Parallel pg_dump is slow by default?\" \/>\n<meta property=\"og:description\" content=\"Short answer: Yes, it is. Being at a customer the last days we wanted to parallel pg_dump a 2TB database. We were quite surprised that it was quite slow and it was not immediately clear why it was. 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