1 大量删除发生后，导致索引页面稀疏，降低了索引使用效率。
2 PostgresQL 9.0之前的版本，vacuum full 会同样导致索引页面稀疏。
3 长时间运行的事务，禁止vacuum对表的清理工作，因而导致页面稀疏状态一直保持。
查看重复索引
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SELECT pg_size_pretty(SUM(pg_relation_size(idx))::BIGINT) AS SIZE, (array_agg(idx))[1] AS idx1, (array_agg(idx))[2] AS idx2, (array_agg(idx))[3] AS idx3, (array_agg(idx))[4] AS idx4FROM ( SELECT indexrelid::regclass AS idx, (indrelid::text ||E'\n'|| indclass::text ||E'\n'|| indkey::text ||E'\n'|| COALESCE(indexprs::text,'')||E'\n' || COALESCE(indpred::text,'')) AS KEY FROM pg_index) subGROUP BY KEY HAVING COUNT(*)>1ORDER BY SUM(pg_relation_size(idx)) DESC; |
表的大小和表中索引个数
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SELECT t.tablename, indexname, c.reltuples AS num_rows, pg_size_pretty(pg_relation_size(quote_ident(t.tablename)::text)) AS table_size, pg_size_pretty(pg_relation_size(quote_ident(indexrelname)::text)) AS index_size, CASE WHEN indisunique THEN 'Y' ELSE 'N' END AS UNIQUE, idx_scan AS number_of_scans, idx_tup_read AS tuples_read, idx_tup_fetch AS tuples_fetchedFROM pg_tables tLEFT OUTER JOIN pg_class c ON t.tablename=c.relnameLEFT OUTER JOIN ( SELECT c.relname AS ctablename, ipg.relname AS indexname, x.indnatts AS number_of_columns, idx_scan, idx_tup_read, idx_tup_fetch, indexrelname, indisunique FROM pg_index x JOIN pg_class c ON c.oid = x.indrelid JOIN pg_class ipg ON ipg.oid = x.indexrelid JOIN pg_stat_all_indexes psai ON x.indexrelid = psai.indexrelid ) AS foo ON t.tablename = foo.ctablenameWHERE t.schemaname='public'ORDER BY 1,2; |
获取每个表的行数，索引和一些关于这些索引的信息（比较详细）
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SELECT pg_class.relname, pg_size_pretty(pg_class.reltuples::BIGINT) AS rows_in_bytes, pg_class.reltuples AS num_rows, COUNT(indexname) AS number_of_indexes, CASE WHEN x.is_unique = 1 THEN 'Y' ELSE 'N' END AS UNIQUE, SUM(CASE WHEN number_of_columns = 1 THEN 1 ELSE 0 END) AS single_column, SUM(CASE WHEN number_of_columns IS NULL THEN 0 WHEN number_of_columns = 1 THEN 0 ELSE 1 END) AS multi_columnFROM pg_namespace LEFT OUTER JOIN pg_class ON pg_namespace.oid = pg_class.relnamespaceLEFT OUTER JOIN (SELECT indrelid, MAX(CAST(indisunique AS INTEGER)) AS is_unique FROM pg_index GROUP BY indrelid) x ON pg_class.oid = x.indrelidLEFT OUTER JOIN ( SELECT c.relname AS ctablename, ipg.relname AS indexname, x.indnatts AS number_of_columns FROM pg_index x JOIN pg_class c ON c.oid = x.indrelid JOIN pg_class ipg ON ipg.oid = x.indexrelid ) AS foo ON pg_class.relname = foo.ctablenameWHERE pg_namespace.nspname='public'AND pg_class.relkind = 'r'GROUP BY pg_class.relname, pg_class.reltuples, x.is_uniqueORDER BY 2; |
补充：postgresql查看表膨胀
查看表膨胀（对所有表产进行膨胀率排序）
SQL文如下：
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SELECT schemaname||'.'||relname as table_name, pg_size_pretty(pg_relation_size(schemaname||'.'||relname)) as table_size, n_dead_tup, n_live_tup, round(n_dead_tup * 100 / (n_live_tup + n_dead_tup),2) AS dead_tup_ratioFROM pg_stat_all_tablesWHERE n_dead_tup >= 1000ORDER BY dead_tup_ratio DESCLIMIT 10; |
以上为个人经验，希望能给大家一个参考，也希望大家多多支持服务器之家。如有错误或未考虑完全的地方，望不吝赐教。
原文链接：https://blog.csdn.net/silenceray/article/details/62045849
