索引膨脹的幾個(gè)來源：

1 大量刪除發(fā)生后，導(dǎo)致索引頁(yè)面稀疏，降低了索引使用效率。

2 PostgresQL 9.0之前的版本，vacuum full 會(huì)同樣導(dǎo)致索引頁(yè)面稀疏。

3 長(zhǎng)時(shí)間運(yùn)行的事務(wù)，禁止vacuum對(duì)表的清理工作，因而導(dǎo)致頁(yè)面稀疏狀態(tài)一直保持。

查看重復(fù)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;