好的，你有一个大表格、索引和长时间执行计划（Plan）需要改进以减少时间。你会写入和删除行数据，PG会写入和删除元组，而表格和索引可能会变得过度膨胀。为便于搜索，PG将索引加载到共享缓存中，因此你需要尽可能地保持索引的干净整洁。对于选择操作，PG会先读取到共享缓存中然后再进行搜索。你可以尝试设置缓冲区内存，并减少索引和表格的膨胀，保持数据库的清洁。
针对此问题，你应该考虑以下事项：
1）仅检查索引重复项并确保你的索引具有良好的选择性：
WITH table_scans as (
SELECT relid,
tables.idx_scan + tables.seq_scan as all_scans,
( tables.n_tup_ins + tables.n_tup_upd + tables.n_tup_del ) as writes,
pg_relation_size(relid) as table_size
FROM pg_stat_user_tables as tables
),
all_writes as (
SELECT sum(writes) as total_writes
FROM table_scans
),
indexes as (
SELECT idx_stat.relid, idx_stat.indexrelid,
idx_stat.schemaname, idx_stat.relname as tablename,
idx_stat.indexrelname as indexname,
idx_stat.idx_scan,
pg_relation_size(idx_stat.indexrelid) as index_bytes,
indexdef ~* 'USING btree' AS idx_is_btree
FROM pg_stat_user_indexes as idx_stat
JOIN pg_index
USING (indexrelid)
JOIN pg_indexes as indexes
ON idx_stat.schemaname = indexes.schemaname
AND idx_stat.relname = indexes.tablename
AND idx_stat.indexrelname = indexes.indexname
WHERE pg_index.indisunique = FALSE
),
index_ratios AS (
SELECT schemaname, tablename, indexname,
idx_scan, all_scans,
round(( CASE WHEN all_scans = 0 THEN 0.0::NUMERIC
ELSE idx_scan::NUMERIC/all_scans * 100 END),2) as index_scan_pct,
writes,
round((CASE WHEN writes = 0 THEN idx_scan::NUMERIC ELSE idx_scan::NUMERIC/writes END),2)
as scans_per_write,
pg_size_pretty(index_bytes) as index_size,
pg_size_pretty(table_size) as table_size,
idx_is_btree, index_bytes
FROM indexes
JOIN table_scans
USING (relid)
),
index_groups AS (
SELECT 'Never Used Indexes' as reason, *, 1 as grp
FROM index_ratios
WHERE
idx_scan = 0
and idx_is_btree
UNION ALL
SELECT 'Low Scans, High Writes' as reason, *, 2 as grp
FROM index_ratios
WHERE
scans_per_write <= 1
and index_scan_pct < 10
and idx_scan > 0
and writes > 100
and idx_is_btree
UNION ALL
SELECT 'Seldom Used Large Indexes' as reason, *, 3 as grp
FROM index_ratios
WHERE
index_scan_pct < 5
and scans_per_write > 1
and idx_scan > 0
and idx_is_btree
and index_bytes > 100000000
UNION ALL
SELECT 'High-Write Large Non-Btree' as reason, index_ratios.*, 4 as grp
FROM index_ratios, all_writes
WHERE
( writes::NUMERIC / ( total_writes + 1 ) ) > 0.02
AND NOT idx_is_btree
AND index_bytes > 100000000
ORDER BY grp, index_bytes DESC )
SELECT reason, schemaname, tablename, indexname,
index_scan_pct, scans_per_write, index_size, table_size
FROM index_groups;
2) 检查是否存在表和索引膨胀问题？
SELECT
current_database(), schemaname, tablename,
ROUND((CASE WHEN otta=0 THEN 0.0 ELSE sml.relpages::FLOAT/otta END)::NUMERIC,1) AS tbloat,
CASE WHEN relpages < otta THEN 0 ELSE bs*(sml.relpages-otta)::BIGINT END AS wastedbytes,
iname,
ROUND((CASE WHEN iotta=0 OR ipages=0 THEN 0.0 ELSE ipages::FLOAT/iotta END)::NUMERIC,1) AS ibloat,
CASE WHEN ipages < iotta THEN 0 ELSE bs*(ipages-iotta) END AS wastedibytes
FROM (
SELECT
schemaname, tablename, cc.reltuples, cc.relpages, bs,
CEIL((cc.reltuples*((datahdr+ma-
(CASE WHEN datahdr%ma=0 THEN ma ELSE datahdr%ma END))+nullhdr2+4))/(bs-20::FLOAT)) AS otta,
COALESCE(c2.relname,'?') AS iname, COALESCE(c2.reltuples,0) AS ituples, COALESCE(c2.relpages,0) AS ipages,
COALESCE(CEIL((c2.reltuples*(datahdr-12))/(bs-20::FLOAT)),0) AS iotta
FROM (
SELECT
ma,bs,schemaname,tablename,
(datawidth+(hdr+ma-(CASE WHEN hdr%ma=0 THEN ma ELSE hdr%ma END)))::NUMERIC AS datahdr,
(maxfracsum*(nullhdr+ma-(CASE WHEN nullhdr%ma=0 THEN ma ELSE nullhdr%ma END))) AS nullhdr2
FROM (
SELECT
schemaname, tablename, hdr, ma, bs,
SUM((1-null_frac)*avg_width) AS datawidth,
MAX(null_frac) AS maxfracsum,
hdr+(
SELECT 1+COUNT(*)/8
FROM pg_stats s2
WHERE null_frac<>0 AND s2.schemaname = s.schemaname AND s2.tablename = s.tablename
) AS nullhdr
FROM pg_stats s, (
SELECT
(SELECT current_setting('block_size')::NUMERIC) AS bs,
CASE WHEN SUBSTRING(v,12,3) IN ('8.0','8.1','8.2') THEN 27 ELSE 23 END AS hdr,
CASE WHEN v ~ 'mingw32' THEN 8 ELSE 4 END AS ma
FROM (SELECT version() AS v) AS foo
) AS constants
GROUP BY 1,2,3,4,5
) AS foo
) AS rs
JOIN pg_class cc ON cc.relname = rs.tablename
JOIN pg_namespace nn ON cc.relnamespace = nn.oid AND nn.nspname = rs.schemaname AND nn.nspname <> 'information_schema'
LEFT JOIN pg_index i ON indrelid = cc.oid
LEFT JOIN pg_class c2 ON c2.oid = i.indexrelid
) AS sml
ORDER BY wastedbytes DESC
3) 您是否清理硬盘上未使用的元组？是时候执行 VACUUM 了吗？
SELECT
relname AS TableName
,n_live_tup AS LiveTuples
,n_dead_tup AS DeadTuples
FROM pg_stat_user_tables;
4) 仔细考虑一下。如果您的数据库中有10条记录，其中8条的id为2，那么这意味着索引的选择性不好，PG将会扫描所有8条记录。但是如果您尝试使用id != 2索引，它就会工作得很好。请尽量设置具有良好选择性的索引。
5) 使用合适的列类型可以节省数据空间。如果您的列可以使用较少kb的类型，请进行转换。
6) 只需检查您的数据库和条件。从页面开始检查未使用的表中的数据，清理索引，检查索引的选择性。尝试使用其他BRIN索引来处理数据，尝试重新创建索引。
act_owner_id的索引。 - frlan