ANALYZE: Interpreting execution stats for index-based access methods
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This article describes how to interpret r_rows
and r_filtered
members in ANALYZE FORMAT=JSON output for cases when the table uses index-based access method.
Index-based access method may employ
- Index Condition Pushdown
- Rowid Filtering
- Regular attached_condition checking
Consider ANALYZE FORMAT=JSON output listing all of the above:
"table": { "table_name": "t1", "access_type": "range", "possible_keys": ..., "key": "INDEX1", ... "rowid_filter": { ... "r_selectivity_pct": n.nnn, }, ... "rows": 123, "r_rows": 125, ... "filtered": 8.476269722, "r_filtered": 100, "index_condition": "cond1", "attached_condition": "cond2" }
Access diagram
The access is performed as follows:
Statistics before the fix for MDEV-18478
Before the fix for MDEV-18478, the counters were counted as follows:
that is,
r_rows
is counted after Index Condition Pushdown check.r_filtered
only counts selectivity of theattached_condition
.- selectivity of the Rowid Filter is in
rowid_filter.r_selectivity_pct
.
Statistics after the fix for MDEV-18478
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