域名預(yù)訂/競(jìng)價(jià)，好“米”不錯(cuò)過

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;

表的大小和表中索引個(gè)數(shù)

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;

獲取每個(gè)表的行數(shù)，索引和一些關(guān)于這些索引的信息（比較詳細(xì)）

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;

補(bǔ)充：postgresql查看表膨脹

查看表膨脹（對(duì)所有表產(chǎn)進(jìn)行膨脹率排序）

SQL文如下：

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;

文章來源：腳本之家

來源地址：https://www.jb51.net/article/204333.htm

申請(qǐng)創(chuàng)業(yè)報(bào)道，分享創(chuàng)業(yè)好點(diǎn)子。點(diǎn)擊此處，共同探討創(chuàng)業(yè)新機(jī)遇！