Re: B-tree index balance?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Ron Johnson <ronljohnsonjr(at)gmail(dot)com>
Cc: pgsql-general <pgsql-general(at)postgresql(dot)org>
Subject: Re: B-tree index balance?
Date: 2024-01-19 16:37:18
Message-ID: 2630263.1705682238@sss.pgh.pa.us
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Ron Johnson <ronljohnsonjr(at)gmail(dot)com> writes:
> On an RDMS which I used in the 1990s and 2000s, b-tree indices of sequences
> would get unbalanced, since every new leaf was added to the far right
> corner of the tree.
> Sure, they would auto-balance *to a degree* during node splits, but all
> those "far-right corner" inserts still left them pretty lopsided.
> Thus, they provided a utility which we could use to determine the
> lopsidedness, and thus decide when to rebuild an index.

> Does Postgresql keep b-tree indexes on sequences fully balanced? If not,
> how do I see how unbalanced they are? (Assume PG12+.)

As far as I know, we don't have a problem of that sort. Continued
insertions will eventually force a split of the root node, which will
rebalance the tree.

regards, tom lane

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