Craig James wrote:
Maybe this is an obviously dumb thing to do,
... and it was. I answered my own question: The problem came from using psql(1) to do something I should have done with pg_dump.
but it looked reasonable to
me. The problem is, the seemingly simple sort below causes a fairly
powerful computer to completely freeze for 5-10 minutes. During the
sort, you can't login, you can't use any shell sessions you already have
open, the Apache server barely works, and even if you do "nice -20 top"
before you start the sort, the top(1) command comes to a halt while the
sort is proceeding! As nearly as I can tell, the sort operation is
causing a swap storm of some sort -- nothing else in my many years of
UNIX/Linux experience can cause a "nice -20" process to freeze.
The sort operation never finishes -- it's always killed by the system.
Once it dies, everything returns to normal.
This is 8.3.0. (Yes, I'll upgrade soon.) Is this a known bug, or do I
have to rewrite this query somehow? Maybe add indexes to all four
columns being sorted?
Thanks!
Craig
=> explain select * from plus order by supplier_id, compound_id, units,
price;
QUERY PLAN
-----------------------------------------------------------------------
Sort (cost=5517200.48..5587870.73 rows=28268100 width=65)
Sort Key: supplier_id, compound_id, units, price
-> Seq Scan on plus (cost=0.00..859211.00 rows=28268100 width=65)
=> \d plus Table "emol_warehouse_1.plus"
Column | Type | Modifiers
---------------+---------------+-----------
supplier_id | integer | supplier_name | text |
compound_id | text | amount | text |
units | text | price | numeric(12,2) |
currency | text | description | text |
sku | text | Indexes:
"i_plus_compound_id" btree (supplier_id, compound_id)
"i_plus_supplier_id" btree (supplier_id)
max_connections = 1000
shared_buffers = 2000MB
work_mem = 256MB
max_fsm_pages = 1000000
max_fsm_relations = 5000
synchronous_commit = off
#wal_sync_method = fdatasync
wal_buffers = 256kB
checkpoint_segments = 30
effective_cache_size = 4GB
Machine: Dell, 8x64-bit CPUs, 8GB ram, Perc6i battery-backed RAID
controller, 8 disks as RAID10
Craig
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