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fix(b6): correct buffer attribution and pct_of_rel calculation #87

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Merged
NikolayS merged 1 commit into from
Feb 10, 2026
Merged

fix(b6): correct buffer attribution and pct_of_rel calculation #87

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19 changes: 15 additions & 4 deletions sql/b6_buffercache.sql
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Original file line number Diff line number Diff line change
Expand Up @@ -17,20 +17,31 @@ with buf as (
count(*) filter (where b.isdirty) as dirty_buffers,
round(
100.0 * count(*) / (
select count(*) from pg_buffercache where relfilenode is not null
select count(*)
from pg_buffercache
where reldatabase = (select oid from pg_database where datname = current_database())
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@tembo tembo Bot Feb 10, 2026

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pct_of_cache denominator currently counts all forks, but the main query filters to b.relforknumber = 0. If the intent is “main fork only” everywhere, consider adding the same filter to the denominator so the percentage stays consistent.

Suggested change
where reldatabase = (select oid from pg_database where datname = current_database())
where reldatabase = (select oid from pg_database where datname = current_database())
and relfilenode is not null
and relforknumber = 0

and relfilenode is not null
),
1
) as pct_of_cache,
round(
100.0 * count(*) / greatest(pg_relation_size(c.oid) / current_setting('block_size')::int, 1),
100.0 * count(*) / greatest(
ceil(pg_relation_size(c.oid)::numeric / current_setting('block_size')::numeric),
1
),
1
) as pct_of_rel,
pg_size_pretty(count(*) * current_setting('block_size')::int) as cached_size,
pg_size_pretty(pg_relation_size(c.oid)) as rel_size
from pg_buffercache as b
join pg_class as c on b.relfilenode = pg_relation_filenode(c.oid)
join pg_class as c
on c.oid = (
select pg_filenode_relation(b.reltablespace, b.relfilenode)
)
Comment on lines +37 to +40
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@tembo tembo Bot Feb 10, 2026

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Minor readability/perf nit: the scalar subquery wrapper around pg_filenode_relation(...) doesn’t buy much here and can be inlined in the join condition.

Suggested change
join pg_class as c
on c.oid = (
select pg_filenode_relation(b.reltablespace, b.relfilenode)
)
on c.oid = pg_filenode_relation(b.reltablespace, b.relfilenode)

join pg_namespace as n on c.relnamespace = n.oid
where b.relfilenode is not null
where b.reldatabase = (select oid from pg_database where datname = current_database())
and b.relfilenode is not null
and b.relforknumber = 0
and n.nspname not in ('pg_catalog', 'information_schema')
and n.nspname !~ '^pg_toast'
group by c.oid, n.nspname, c.relname, c.relkind
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