Re: VACUUM FULL ANALYSE hanging

Peter Koczan <pjkoczan@xxxxxxxxx> · Wed, 02 May 2007 10:12:46 -0500

I've noticed in my own experiments and experiences with VACUUM FULL that 
it tries to reindex all the indexes to compress them. While a good idea, 
this unfortunately takes a *long* time.

You should check two things. First, the server CPU usage should be high 
(~100% if on a single core). Second, check the contents of the pg_locks 
view. It should hold exclusive locks on all the indexes (though it's 
ordered by oid, so you might have to check pg_class or something else to 
get the actual table/index name). If it's truly hanging/deadlocking, the 
locks won't be granted, and the CPU usage will be low.

In my experiences, doing a dump/restore was far faster, but this method 
creates downtime. (e.g. a 10 GB database took 2 hours to restore, while 
reindexing/vacuuming full was still on the same table after 4 hours).

If anyone can shed some light onto why reindexing/vacuuming full takes 
so long, I'd like to know.

Peter

Gabriele Bartolini wrote:
Hi guys,

   I am having problems with freeing disk space after a massive delete 
operation on a table that had approximately 80 million record. I 
ran the following command, by setting the vacuum memory to 
approximately a GigaByte:

SET vacuum_mem TO 1024000
VACUUM FULL ANALYSE VERBOSE oltp.requests

Here is what I get:

There were 34221203 unused item pointers.
Total free space (including removable row versions) is 8969616624 bytes.
1129827 pages are or will become empty, including 0 at the end of the 
table.
1337307 pages containing 8964065020 free bytes are potential move 
destinations.
CPU 16.03s/9.12u sec elapsed 219.47 sec.
INFO:  index "requests_pkey" now contains 20075362 row versions in 
327419 pages
DETAIL:  8211835 index row versions were removed.
217782 index pages have been deleted, 217782 are currently reusable.
CPU 5.38s/12.53u sec elapsed 100.80 sec.
INFO:  index "idx_oltp_requests_access_date" now contains 20075362 row 
versions in 491725 pages
DETAIL:  8211835 index row versions were removed.
426501 index pages have been deleted, 426501 are currently reusable.
CPU 14.96s/13.47u sec elapsed 200.91 sec.
INFO:  index "idx_oltp_requests_access_time" now contains 20075362 row 
versions in 343915 pages
DETAIL:  8211835 index row versions were removed.
213612 index pages have been deleted, 213612 are currently reusable.
CPU 6.32s/14.03u sec elapsed 111.24 sec.
INFO:  index "idx_oltp_requests_referer" now contains 20075362 row 
versions in 470822 pages
DETAIL:  8211835 index row versions were removed.
376873 index pages have been deleted, 376873 are currently reusable.
CPU 18.85s/17.18u sec elapsed 265.25 sec.
INFO:  index "idx_oltp_requests_session" now contains 20075362 row 
versions in 611141 pages
DETAIL:  8211835 index row versions were removed.
478827 index pages have been deleted, 478827 are currently reusable.
CPU 16.83s/14.33u sec elapsed 258.47 sec.
INFO:  index "idx_oltp_requests_status_code" now contains 20075362 row 
versions in 690337 pages
DETAIL:  8211835 index row versions were removed.
600953 index pages have been deleted, 600953 are currently reusable.
CPU 34.37s/24.44u sec elapsed 297.21 sec.
INFO:  index "idx_oltp_requests_url" now contains 20075362 row 
versions in 336075 pages
DETAIL:  8211835 index row versions were removed.
73821 index pages have been deleted, 73821 are currently reusable.
CPU 17.06s/28.14u sec elapsed 319.16 sec.
   But here, the command simply hangs.

   The table description is:

htminer=> \d oltp.requests
                        Tabella "oltp.requests"
      Colonna       |            Tipo             |    Modificatori
--------------------+-----------------------------+--------------------
 id_request         | integer                     | not null
 id_session         | integer                     |
 access_time        | timestamp(0) with time zone | not null
 request_method     | numeric(2,0)                | not null default 1
 http_version_major | numeric(1,0)                | not null default 1
 http_version_minor | numeric(1,0)                | not null default 1
 status_code        | numeric(3,0)                | not null
 bytes              | integer                     |
 time_taken         | numeric(3,0)                |
 id_url             | integer                     | not null
 id_referer         | integer                     |
 content_language   | character(2)                |
 dwell_time         | smallint                    | not null default 1
 request_type       | numeric(1,0)                |
Indici:
    "requests_pkey" PRIMARY KEY, btree (id_request), tablespace 
"htminer_oltp"
    "idx_oltp_requests_access_date" btree (date_trunc('day'::text, 
timezone('UTC'::text, access_time))), tablespace "htminer_oltp"
    "idx_oltp_requests_access_time" btree (access_time), tablespace 
"htminer_oltp"
    "idx_oltp_requests_referer" btree (id_referer), tablespace 
"htminer_oltp"
    "idx_oltp_requests_session" btree (id_session, status_code), 
tablespace "htminer_oltp"
    "idx_oltp_requests_status_code" btree (status_code), tablespace 
"htminer_oltp"
    "idx_oltp_requests_url" btree (id_url), tablespace "htminer_oltp"
Vincoli di controllo:
    "requests_bytes_check" CHECK (bytes >= 0)
    "requests_dwell_time_check" CHECK (dwell_time >= 0)
    "requests_id_request_check" CHECK (id_request > 0)
    "requests_request_method_check" CHECK (request_method > 0::numeric)
    "requests_request_type_check" CHECK (request_type > 0::numeric)
Vincoli di integrità referenziale
    "requests_id_referer_fkey" FOREIGN KEY (id_referer) REFERENCES 
oltp.urls(id_url) ON UPDATE CASCADE ON DELETE CASCADE
    "requests_id_session_fkey" FOREIGN KEY (id_session) REFERENCES 
oltp.sessions(id_session) ON UPDATE CASCADE ON DELETE CASCADE
    "requests_id_url_fkey" FOREIGN KEY (id_url) REFERENCES 
oltp.urls(id_url) ON UPDATE CASCADE ON DELETE CASCADE
Tablespace: "htminer_oltp"
Should I drop the indexes and re-create them?

Thanks,
Gabriele

--
Gabriele Bartolini - Istruttore Informatico - Comune di Prato
Sistema Informativo - Servizi di E-Government e Open-Source
g.bartolini@xxxxxxxxxxxxxxx <mailto:g.bartolini@xxxxxxxxxxxxxxx> - 
www.comune.prato.it <http://www.comune.prato.it/> - www.htminer.it 
<http://www.htminer.it/>