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 idx4
FROM (
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) sub
GROUP BY KEY HAVING COUNT(*)>1
ORDER BY SUM(pg_relation_size(idx)) DESC;
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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_fetched
FROM pg_tables t
LEFT OUTER JOIN pg_class c ON t.tablename=c.relname
LEFT 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.ctablename
WHERE t.schemaname='public'
ORDER BY 1,2;
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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_column
FROM pg_namespace
LEFT OUTER JOIN pg_class ON pg_namespace.oid = pg_class.relnamespace
LEFT OUTER JOIN
(SELECT indrelid,
MAX(CAST(indisunique AS INTEGER)) AS is_unique
FROM pg_index
GROUP BY indrelid) x
ON pg_class.oid = x.indrelid
LEFT 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.ctablename
WHERE
pg_namespace.nspname='public'
AND pg_class.relkind = 'r'
GROUP BY pg_class.relname, pg_class.reltuples, x.is_unique
ORDER BY 2;
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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_ratio
FROM
pg_stat_all_tables
WHERE
n_dead_tup >= 1000
ORDER BY dead_tup_ratio DESC
LIMIT 10;
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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