Hi, On 01/05/2016 10:38 AM, Tomas Vondra wrote:
Hi,
...
There shouldn't be a difference between the two approaches (although I guess there could be if one left a larger pending list than the other, as pending lists is very space inefficient), but since you included 9.5 in your test I thought it would be interesting to see how either patched version under 9.6 compared to 9.5.Well, turns out there's a quite significant difference, actually. The index sizes I get (quite stable after multiple runs): 9.5 : 2428 MB 9.6 + alone cleanup : 730 MB 9.6 + pending lock : 488 MB So that's quite a significant difference, I guess. The load duration for each version look like this: 9.5 : 1415 seconds 9.6 + alone cleanup : 1310 seconds 9.6 + pending lock : 1380 seconds I'd say I'm happy with sacrificing ~5% of time in exchange for ~35% reduction of index size. The size of the index on 9.5 after VACUUM FULL (so pretty much the smallest index possible) is 440MB, which suggests the "pending lock" patch does a quite good job. The gin_metapage_info at the end of one of the runs (pretty much all the runs look exactly the same) looks like this: pending lock alone cleanup 9.5 -------------------------------------------------------- pending_head 2 2 310460 pending_tail 338 345 310806 tail_free_size 812 812 812 n_pending_pages 330 339 347 n_pending_tuples 1003 1037 1059 n_total_pages 2 2 2 n_entry_pages 1 1 1 n_data_pages 0 0 0 n_entries 0 0 0 version 2 2 2 So almost no difference, except for the pending_* attributes, and even in that case the values are only different for 9.5 branch. Not sure what conclusion to draw from this - maybe it's necessary to collect the function input while the load is running (but that'd be tricky to process, I guess).
Are we going to anything about this? While the bug is present in 9.5 (and possibly other versions), fixing it before 9.6 gets out seems important because reproducing it there is rather trivial (while I've been unable to reproduce it on 9.5).
regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
