Re: How can i be certain autovacuum is causing reuse if table still grows - Mailing list pgsql-admin

Le lun. 3 août 2020 à 23:36, Sidney Aloisio Ferreira Pryor <sidney@tjrj.jus.br> a écrit :

Hi Keith, how are you?

Hope you are very fine.

As i promissed we ran vacuum full on that table on a test environment similar to production and it took 11 hours to complete.

It reduced the original table segment from 2.3TB to 100GB as below (note that it is still growing...).

So we are now proposing to our Direction a maintenance window to vacuum full production.

Original:

 table_schema |     table_name      | total_size | data_size | external_size

--------------+---------------------+------------+-----------+---------------

 public       | flip_pagina_edicao  | 4578 GB    | 2880 GB   | 1699 GB

Copy of Orginal  (after vacuum full):

 table_schema |     table_name      | total_size | data_size | external_size

--------------+---------------------+------------+-----------+---------------

 public       | flip_pagina_edicao  | 180 GB    | 100 GB   | 80 GB

In meantime if you could please help us understand some curious facts below about vacuum verbose (not full).

I am running on production another vacuum verbose (not full) because that first one stucked on the same indexes for 3 days.

But now is on a 3rd sequential scan of all indexes of that table followed by a scan on the table itself.

It is not finishing even completing scans.

1) Why it is scanning again and not finishing vacuum?

Your maintenance_work_mem parameter value is probably too low.

2) I noticed that on all scans it is taking 12 hours only on an index on a bpchar(1) column (character(1) DEFAULT 'N'::bpchar).

All other indexes and even the table it self are running too much faster, can you guess a reason for this?

CREATE INDEX ocrindex

  ON public.flip_pagina_edicao

  USING btree

  (ocr COLLATE pg_catalog."default");

Not used, so not in cache? or much bigger than the other ones?

3) And is repeatly scanning 11.184.520 or 521 or 528 row versions.

Why does it not end and scans again the same amount of row versions?

Well, VACUUM is a multi-steps operation. It first scans the table and puts every tid that needs to be deleted in memory. Once done, il will scan indexes. But if there's more TID than memory can hold, it will have to do multiple scans of the table and the indexes. It seems clear in your case that, when VACUUM finds 11184520 TID, memory is full. By the way, memory is limited by a parameter named maintenance_work_mem. So what is its current value?

flip=# vacuum verbose flip_pagina_edicao;

INFO:  vacuuming "public.flip_pagina_edicao"

INFO:  scanned index "id_caderno" to remove 11184520 row versions

DETAIL:  CPU 155.34s/540.40u sec elapsed 1101.49 sec

INFO:  scanned index "ordem_index" to remove 11184520 row versions

DETAIL:  CPU 253.35s/870.77u sec elapsed 1962.36 sec

INFO:  scanned index "primary00024" to remove 11184520 row versions

DETAIL:  CPU 134.10s/478.79u sec elapsed 922.02 sec

INFO:  scanned index "ordem" to remove 11184520 row versions

DETAIL:  CPU 265.16s/932.90u sec elapsed 1878.20 sec

INFO:  scanned index "flip_pagina_edicao_pkey" to remove 11184520 row versions

DETAIL:  CPU 149.51s/523.42u sec elapsed 949.68 sec

INFO:  scanned index "flip_flippagedic_idcaderno" to remove 11184520 row versions

DETAIL:  CPU 460.19s/1171.75u sec elapsed 2696.89 sec

INFO:  scanned index "nomepdfindex" to remove 11184520 row versions

DETAIL:  CPU 598.88s/1286.84u sec elapsed 3543.26 sec

INFO:  scanned index "ocrindex" to remove 11184520 row versions

DETAIL:  CPU 25657.30s/18907.82u sec elapsed 46652.49 sec

INFO:  scanned index "idr_documento_index" to remove 11184520 row versions

DETAIL:  CPU 321.96s/968.75u sec elapsed 2004.91 sec

INFO:  "flip_pagina_edicao": removed 11184520 row versions in 3762529 pages

DETAIL:  CPU 165.65s/95.06u sec elapsed 647.49 sec

INFO:  scanned index "id_caderno" to remove 11184521 row versions

DETAIL:  CPU 175.89s/461.26u sec elapsed 1098.74 sec

INFO:  scanned index "ordem_index" to remove 11184521 row versions

DETAIL:  CPU 301.57s/887.26u sec elapsed 2052.44 sec

INFO:  scanned index "primary00024" to remove 11184521 row versions

DETAIL:  CPU 150.12s/461.92u sec elapsed 947.74 sec

INFO:  scanned index "ordem" to remove 11184521 row versions

DETAIL:  CPU 286.29s/896.03u sec elapsed 1954.21 sec

INFO:  scanned index "flip_pagina_edicao_pkey" to remove 11184521 row versions

DETAIL:  CPU 140.75s/423.38u sec elapsed 901.04 sec

INFO:  scanned index "flip_flippagedic_idcaderno" to remove 11184521 row versions

DETAIL:  CPU 455.24s/1043.27u sec elapsed 2551.54 sec

INFO:  scanned index "nomepdfindex" to remove 11184521 row versions

DETAIL:  CPU 644.78s/1163.80u sec elapsed 3469.67 sec

INFO:  scanned index "ocrindex" to remove 11184521 row versions

DETAIL:  CPU 25951.95s/18712.36u sec elapsed 49880.37 sec

INFO:  scanned index "idr_documento_index" to remove 11184521 row versions

DETAIL:  CPU 274.05s/710.37u sec elapsed 1799.98 sec

INFO:  "flip_pagina_edicao": removed 11184521 row versions in 2358457 pages

DETAIL:  CPU 68.83s/36.81u sec elapsed 353.40 sec

INFO:  scanned index "id_caderno" to remove 11184528 row versions

DETAIL:  CPU 156.47s/372.75u sec elapsed 1022.31 sec

INFO:  scanned index "ordem_index" to remove 11184528 row versions

DETAIL:  CPU 257.13s/669.86u sec elapsed 2057.05 sec

INFO:  scanned index "primary00024" to remove 11184528 row versions

DETAIL:  CPU 116.29s/319.86u sec elapsed 842.55 sec

INFO:  scanned index "ordem" to remove 11184528 row versions

DETAIL:  CPU 232.78s/562.22u sec elapsed 2676.35 sec

INFO:  scanned index "flip_pagina_edicao_pkey" to remove 11184528 row versions

DETAIL:  CPU 91.21s/241.00u sec elapsed 875.27 sec

INFO:  scanned index "flip_flippagedic_idcaderno" to remove 11184528 row versions

DETAIL:  CPU 285.71s/585.63u sec elapsed 2593.08 sec

INFO:  scanned index "nomepdfindex" to remove 11184528 row versions

DETAIL:  CPU 413.55s/692.77u sec elapsed 3843.78 sec

Thank you.

Sidney Pryor.

--

Guillaume.