On 28.06.2018 05:00, Peter Geoghegan wrote:
On Tue, Jun 26, 2018 at 11:40 PM, Andrey V. Lepikhov
<a.lepik...@postgrespro.ru> wrote:
I still believe that the patch for physical TID ordering in btree:
1) has its own value, not only for target deletion,
2) will require only a few local changes in my code,
and this patches can be developed independently.
I want to be clear on something now: I just don't think that this
patch has any chance of getting committed without something like my
own patch to go with it. The worst case for your patch without that
component is completely terrible. It's not really important for you to
actually formally make it part of your patch, so I'm not going to
insist on that or anything, but the reality is that my patch does not
have independent value -- and neither does yours.
As I wrote before in the last email, I will integrate TID sorting to my
patches right now. Please, give me access to the last version of your
code, if it possible.
You can track the progress at https://github.com/danolivo/postgres git
repository
I'm sorry if that sounds harsh, but this is a difficult, complicated
project. It's better to be clear about this stuff earlier on.
Ok. It is clear now.
I prepare third version of the patches. Summary:
1. Mask DEAD tuples at a page during consistency checking (See comments for
the mask_dead_tuples() function).
2. Still not using physical TID ordering.
3. Index cleanup() after each quick_vacuum_index() call was excluded.
How does this patch affect opportunistic pruning in particular? Not
being able to immediately reclaim tuple space in the event of a dead
hot chain that is marked LP_DEAD could hurt quite a lot, including
with very common workloads, such as pgbench (pgbench accounts tuples
are quite a lot wider than a raw item pointer, and opportunistic
pruning is much more important than vacuuming). Is that going to be
acceptable, do you think? Have you measured the effects? Can we do
something about it, like make pruning behave differently when it's
opportunistic?
This is the most "tasty" part of the work. I plan some experimental
research on it at the end of patches developing (including TID sort)
and parametrized opportunistic pruning for flexibility of switching
between strategies on the fly.
My current opinion on this question: we can develop flexible strategy
based on parameters: free space at a block, frequency of UPDATE/DELETE
queries, percent of DEAD tuples in a block/relation.
Background cleaner, raised by heap_page_prune(), give an opportunity for
using different ways for each block or relation.
This technique should be able to configure from fully non-storage DEAD
tuples+vacuum to all-storage DEAD tuples+target deletion by DB admin.
Are you aware of the difference between _bt_delitems_delete() and
_bt_delitems_vacuum(), and the considerations for hot standby? I think
that that's another TODO list item for this patch.
Ok
--
Andrey Lepikhov
Postgres Professional:
https://postgrespro.com
The Russian Postgres Company
