Thanks to Justin for the clarification around pgstatindex:
Staging:
version2
tree_level1
index_size425984
root_block_no3
internal_pages1
leaf_pages50
empty_pages0
deleted_pages0
avg_leaf_density70.86
leaf_fragmentation16
Production:
version2
tree_level1
index_size360448
root_block_no3
internal_pages1
leaf_pages41
empty_pages0
deleted_pages1
avg_leaf_density60.44
leaf_fragmentation39.02
On 11/4/19, 3:07 PM, "Peter Geoghegan" <pg@xxxxxxx> wrote:
On Mon, Nov 4, 2019 at 11:56 AM Justin Pryzby <pryzby@xxxxxxxxxxxxx> wrote:
> I think it's because some heap pages are being visited many times, due to the
> index tuples being badly "fragmented". Note, I'm not talking about
> fragmentation of index *pages*, which is what pgstattuple reports (which
> wouldn't have nearly so detrimental effect). I could probably say that the
> index tuples are badly "correlated" with the heap.
But this is a unique index, and Scott indicates that the problem seems
to go away for a while following a REINDEX.
> In PG v12 you can use REINDEX CONCURRENTLY (but beware there's a crash
> affecting its progress reporting, fix to be included in v12.1).
PG v12 will store B-Tree duplicates in heap TID order, so if that's
the problem then upgrading to v12 (and REINDEXing if the upgrade was
performed using pg_upgrade) will fix it for good.
--
Peter Geoghegan
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