索引膨脹的幾個來源：

1 大量刪除發生后，導致索引頁面稀疏，降低了索引使用效率。

2 PostgresQL 9.0之前的版本，vacuum full 會同樣導致索引頁面稀疏。

3 長時間運行的事務，禁止vacuum對表的清理工作，因而導致頁面稀疏狀態一直保持。

查看重復索引

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;