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<title>[筆記] 測試 postgresql 的pg_prewarm 對效能的影響 / test pg_prewarm in postgresql 11 </title>
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<span class="date">20 December</span> <span> / </span>
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<a href="https://github.com/changchichung" title="Posts by Eric Chang" rel="author">Eric Chang</a>
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<a href="/categories/%E7%AD%86%E8%A8%98">筆記</a>
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<div class='entry-header'>
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<h1 class='entry-title'> [筆記] 測試 postgresql 的pg_prewarm 對效能的影響 / test pg_prewarm in postgresql 11</h1>
|
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</div>
|
|
|
<div class="entry-container">
|
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<div class="entry-content">
|
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<article>
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<p>老闆提到想要把新系統的 postgresql 資料庫都撈到記憶體裡面</p>
|
|
|
|
|
|
<p>但是否決了我提出的ramdisk 作法(因為當機的話，資料就沒了)</p>
|
|
|
|
|
|
<p>在找資料的時候，發現了這個postgresql 的 pg_prewarm extension</p>
|
|
|
|
|
|
<p>好像有點意思？就來測試看看吧！</p>
|
|
|
|
|
|
<p>只是目前還不知道該怎麼解讀測試的數據就是了…</p>
|
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|
|
|
|
<p>幹！林北真的不是 DBA 啦 =.=</p>
|
|
|
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|
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<p>安裝系統、postgresql 資料庫什麼的就不提了，那不是這次的重點</p>
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<h4 id="修改-postgresql-conf">修改 postgresql.conf</h4>
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<p>編輯postgresql.conf，開啟平行處理以及設定可用記憶體容量</p>
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<p>這台測試機的環境是一台三代i7 , 24G RAM , 240G SSD，安裝debian 10(buster)</p>
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<pre><code># load libiriaes
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# 其實這次不會用到pg_stat_statements ，不過出於習慣，還是加入開機自動載入吧
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shared_preload_libraries = 'pg_stat_statements'
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#------------------------------------------------------------------------------
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# CUSTOMIZED OPTIONS
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|
#------------------------------------------------------------------------------
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max_connections = 20
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|
shared_buffers = 6GB
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|
|
effective_cache_size = 18GB
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|
|
maintenance_work_mem = 1536MB
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|
checkpoint_completion_target = 0.7
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|
wal_buffers = 16MB
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|
default_statistics_target = 100
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|
random_page_cost = 1.1
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effective_io_concurrency = 200
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work_mem = 78643kB
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min_wal_size = 1GB
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max_wal_size = 2GB
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|
max_worker_processes = 8
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|
max_parallel_workers_per_gather = 4
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|
max_parallel_workers = 8
|
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|
</code></pre>
|
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|
<p>重新啟動postgresql ，準備開始測試囉！</p>
|
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<p>轉換成 postgres 身份後，進入 psql</p>
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<h4 id="建立測試資料庫">建立測試資料庫</h4>
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<pre><code>postgres=# create database test;
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CREATE DATABASE
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postgres=#
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</code></pre>
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<h4 id="連接測試資料庫-建立pg-prewarm-extension">連接測試資料庫、建立pg_prewarm extension</h4>
|
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<pre><code>postgres=# \c test ;
|
|
|
You are now connected to database "test" as user "postgres".
|
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test=# CREATE EXTENSION pg_prewarm;
|
|
|
CREATE EXTENSION
|
|
|
test=#
|
|
|
</code></pre>
|
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|
|
<h4 id="建立測試資料表-塞入500萬筆資料">建立測試資料表，塞入500萬筆資料</h4>
|
|
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|
|
<pre><code>test=# \timing
|
|
|
Timing is on.
|
|
|
test=# CREATE TABLE test_tbl AS
|
|
|
SELECT floor(random() * (9923123) + 1)::int FROM generate_series(1, 5000000) AS id;
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|
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SELECT 5000000
|
|
|
Time: 2940.602 ms (00:02.941)
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test=#
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|
</code></pre>
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<h4 id="檢查看看剛剛建立的table-用了多少空間">檢查看看剛剛建立的table 用了多少空間</h4>
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<p>哎呀，看起來用得不多啊</p>
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|
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<pre><code>test=# SELECT pg_size_pretty(pg_relation_size('test_tbl'));
|
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173 MB
|
|
|
</code></pre>
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<p><strong>玩大一點，塞個一億筆資料好了</strong></p>
|
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<pre><code>test=# drop table test_tbl;
|
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|
Time: 0.361 ms
|
|
|
test=# CREATE TABLE test_tbl AS
|
|
|
SELECT floor(random() * (99343) + 1)::int FROM generate_series(1, 100000000) AS id;
|
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SELECT 100000000
|
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|
Time: 6321.415 ms (00:06.321)
|
|
|
|
|
|
test=# SELECT pg_size_pretty(pg_relation_size('test_tbl'));
|
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pg_size_pretty | 3457 MB
|
|
|
|
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|
Time: 0.589 ms
|
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|
test=#
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</code></pre>
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<p>好，現在資料庫長到3457MB了</p>
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<p>先來執行一些初步的取得基本數據</p>
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<pre><code>test=# explain (analyze,buffers) select count(*) from test_tbl;
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QUERY PLAN
|
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|
------------------------------------------------------------------------------------------------------------------------
|
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|
Finalize Aggregate (cost=755978.52..755978.53 rows=1 width=8) (actual time=3331.917..3331.918 rows=1 loops=1)
|
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Buffers: shared hit=160 read=442318
|
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-> Gather (cost=755978.10..755978.51 rows=4 width=8) (actual time=3331.876..3333.674 rows=5 loops=1)
|
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Workers Planned: 4
|
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|
Workers Launched: 4
|
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|
Buffers: shared hit=160 read=442318
|
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-> Partial Aggregate (cost=754978.10..754978.11 rows=1 width=8) (actual time=3329.279..3329.280 rows=1 loops=5)
|
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Buffers: shared hit=160 read=442318
|
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-> Parallel Seq Scan on test_tbl (cost=0.00..692478.08 rows=25000008 width=0) (actual time=0.029..1924.601 rows=20000000 loops=5)
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Buffers: shared hit=160 read=442318
|
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Planning Time: 0.040 ms
|
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Execution Time: 3333.729 ms
|
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(12 rows)
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(END)
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</code></pre>
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<p>可以看到打中buffer 的部份其實很少，只有 160 ，大部分都是讀進去buffer (442318)</p>
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<p>來看看 buffer 的使用狀況</p>
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<pre><code>test=# CREATE EXTENSION pg_buffercache;
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CREATE EXTENSION
|
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test=# select c.relname,pg_size_pretty(count(*) * 8192) as buffered,
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test-# round(100.0 * count(*) / (
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test(# select setting from pg_settings
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test(# where name='shared_buffers')::integer,1)
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test-# as buffer_percent,
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test-# round(100.0*count(*)*8192 / pg_table_size(c.oid),1) as percent_of_relation
|
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test-# from pg_class c inner join pg_buffercache b on b.relfilenode = c.relfilenode inner
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test-# join pg_database d on ( b.reldatabase =d.oid and d.datname =current_database())
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test-# group by c.oid,c.relname order by 3 desc limit 10;
|
|
|
relname | buffered | buffer_percent | percent_of_relation
|
|
|
--------------+------------+----------------+---------------------
|
|
|
test_tbl | 18 MB | 0.3 | 0.5
|
|
|
pg_am | 8192 bytes | 0.0 | 20.0
|
|
|
pg_index | 24 kB | 0.0 | 37.5
|
|
|
pg_amproc | 32 kB | 0.0 | 50.0
|
|
|
pg_cast | 16 kB | 0.0 | 33.3
|
|
|
pg_depend | 64 kB | 0.0 | 13.3
|
|
|
pg_amop | 48 kB | 0.0 | 54.5
|
|
|
pg_namespace | 8192 bytes | 0.0 | 20.0
|
|
|
pg_opclass | 16 kB | 0.0 | 28.6
|
|
|
pg_aggregate | 8192 bytes | 0.0 | 16.7
|
|
|
(10 rows)
|
|
|
|
|
|
Time: 148.719 ms
|
|
|
test=#
|
|
|
</code></pre>
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<p>可以看到這個 test_tbl 只有0.5% 被撈到shared_buffers 裡面</p>
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<p>接下來就把這個table全部推到shared_buffers 裡面去</p>
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|
<pre><code>test=# select pg_prewarm('test_tbl','buffer');
|
|
|
pg_prewarm
|
|
|
------------
|
|
|
442478
|
|
|
(1 row)
|
|
|
|
|
|
Time: 1938.043 ms (00:01.938)
|
|
|
test=#
|
|
|
</code></pre>
|
|
|
|
|
|
<p>然後再來看一次shared_buffers的使用狀況</p>
|
|
|
|
|
|
<pre><code>test=# select c.relname,pg_size_pretty(count(*) * 8192) as buffered,
|
|
|
round(100.0 * count(*) / (
|
|
|
select setting from pg_settings
|
|
|
where name='shared_buffers')::integer,1)
|
|
|
as buffer_percent,
|
|
|
round(100.0*count(*)*8192 / pg_table_size(c.oid),1) as percent_of_relation
|
|
|
from pg_class c inner join pg_buffercache b on b.relfilenode = c.relfilenode inner
|
|
|
join pg_database d on ( b.reldatabase =d.oid and d.datname =current_database())
|
|
|
group by c.oid,c.relname order by 3 desc limit 10;
|
|
|
relname | buffered | buffer_percent | percent_of_relation
|
|
|
--------------+------------+----------------+---------------------
|
|
|
test_tbl | 3457 MB | 56.3 | 100.0
|
|
|
pg_am | 8192 bytes | 0.0 | 20.0
|
|
|
pg_index | 24 kB | 0.0 | 37.5
|
|
|
pg_amproc | 32 kB | 0.0 | 50.0
|
|
|
pg_cast | 16 kB | 0.0 | 33.3
|
|
|
pg_depend | 64 kB | 0.0 | 13.3
|
|
|
pg_amop | 48 kB | 0.0 | 54.5
|
|
|
pg_namespace | 8192 bytes | 0.0 | 20.0
|
|
|
pg_opclass | 16 kB | 0.0 | 28.6
|
|
|
pg_aggregate | 8192 bytes | 0.0 | 16.7
|
|
|
(10 rows)
|
|
|
|
|
|
Time: 2778.354 ms (00:02.778)
|
|
|
test=#
|
|
|
</code></pre>
|
|
|
|
|
|
<p>OK ，可以看到 test_tbl 已經通通被載入 shared_buffers 中</p>
|
|
|
|
|
|
<p><strong>buffered 表示表格被載入shared_buffers的大小</strong></p>
|
|
|
|
|
|
<p><strong>buffer_percent 表示這個表格佔用多少shared_buffers 的比例</strong></p>
|
|
|
|
|
|
<p><strong>percent_of_relation 表示這個表格有多少比例被載入 shared_buffers</strong></p>
|
|
|
|
|
|
<p>再來跑一次explain看看狀況</p>
|
|
|
|
|
|
<pre><code>test=# explain (analyze,buffers) select count(*) from test_tbl;
|
|
|
Time: 3551.785 ms (00:03.552)
|
|
|
Finalize Aggregate (cost=755978.52..755978.53 rows=1 width=8) (actual time=3427.286..3427.287 rows=1 loops=1)
|
|
|
Buffers: shared hit=442478
|
|
|
-> Gather (cost=755978.10..755978.51 rows=4 width=8) (actual time=3427.215..3551.326 rows=5 loops=1)
|
|
|
Workers Planned: 4
|
|
|
Workers Launched: 4
|
|
|
Buffers: shared hit=442478
|
|
|
-> Partial Aggregate (cost=754978.10..754978.11 rows=1 width=8) (actual time=3423.659..3423.659 rows=1 loops=5)
|
|
|
Buffers: shared hit=442478
|
|
|
-> Parallel Seq Scan on test_tbl (cost=0.00..692478.08 rows=25000008 width=0) (actual time=0.017..1976.744 rows=20000000 loops=5)
|
|
|
Buffers: shared hit=442478
|
|
|
Planning Time: 0.039 ms
|
|
|
Execution Time: 3551.365 ms
|
|
|
(12 rows)
|
|
|
|
|
|
</code></pre>
|
|
|
|
|
|
<p>這邊就可以看到都是從buffer 讀出來所以 hit=442478</p>
|
|
|
|
|
|
<p>看樣子表格還是太小，所以沒有完全發揮？那再來把表格加大！</p>
|
|
|
|
|
|
<p>先重開一次 postgresql 清除buffer</p>
|
|
|
|
|
|
<p>然後重新建立表格</p>
|
|
|
|
|
|
<pre><code>test=# drop table test_tbl;
|
|
|
DROP TABLE
|
|
|
Time: 297.493 ms
|
|
|
test=# CREATE TABLE test_tbl AS
|
|
|
test-# SELECT floor(random() * (993343) + 1)::int FROM generate_series(1, 300000000) AS id;
|
|
|
SELECT 300000000
|
|
|
Time: 290660.607 ms (04:50.661)
|
|
|
test=#
|
|
|
</code></pre>
|
|
|
|
|
|
<p>一樣，看看用了多少容量</p>
|
|
|
|
|
|
<pre><code>test=# SELECT pg_size_pretty(pg_relation_size('test_tbl'));
|
|
|
pg_size_pretty
|
|
|
----------------
|
|
|
10 GB
|
|
|
(1 row)
|
|
|
|
|
|
Time: 0.474 ms
|
|
|
test=#
|
|
|
</code></pre>
|
|
|
|
|
|
<p>哇哈哈，用了10G ，這次還不撐爆你！</p>
|
|
|
|
|
|
<p>跑explain 看看狀況</p>
|
|
|
|
|
|
<pre><code>test=# explain (analyze,buffers) select count(*) from test_tbl;
|
|
|
Time: 22909.065 ms (00:22.909)
|
|
|
|
|
|
QUERY PLAN
|
|
|
---------------------------------------------------------------------------------------------------------------------------
|
|
|
Finalize Aggregate (cost=2265934.72..2265934.73 rows=1 width=8) (actual time=22906.045..22906.045 rows=1 loops=1)
|
|
|
Buffers: shared hit=2080 read=1325354 dirtied=1295425 written=1295265
|
|
|
-> Gather (cost=2265934.30..2265934.71 rows=4 width=8) (actual time=22905.997..22908.522 rows=5 loops=1)
|
|
|
Workers Planned: 4
|
|
|
Workers Launched: 4
|
|
|
Buffers: shared hit=2080 read=1325354 dirtied=1295425 written=1295265
|
|
|
-> Partial Aggregate (cost=2264934.30..2264934.31 rows=1 width=8) (actual time=22903.473..22903.474 rows=1 loops=5)
|
|
|
Buffers: shared hit=2080 read=1325354 dirtied=1295425 written=1295265
|
|
|
-> Parallel Seq Scan on test_tbl (cost=0.00..2077434.24 rows=75000024 width=0) (actual time=0.040..18374.277 rows=60000000 loops=5)
|
|
|
Buffers: shared hit=2080 read=1325354 dirtied=1295425 written=1295265
|
|
|
Planning Time: 0.094 ms
|
|
|
Execution Time: 22908.571 ms
|
|
|
(12 rows)
|
|
|
|
|
|
</code></pre>
|
|
|
|
|
|
<p>看一下現在 shared_buffers 使用狀況</p>
|
|
|
|
|
|
<p>可以看到這個 test_tbl 幾乎沒被放入 shared_buffers 中</p>
|
|
|
|
|
|
<pre><code>test=# select c.relname,pg_size_pretty(count(*) * 8192) as buffered,
|
|
|
round(100.0 * count(*) / (
|
|
|
select setting from pg_settings
|
|
|
where name='shared_buffers')::integer,1)
|
|
|
as buffer_percent,
|
|
|
round(100.0*count(*)*8192 / pg_table_size(c.oid),1) as percent_of_relation
|
|
|
from pg_class c inner join pg_buffercache b on b.relfilenode = c.relfilenode inner
|
|
|
join pg_database d on ( b.reldatabase =d.oid and d.datname =current_database())
|
|
|
group by c.oid,c.relname order by 3 desc limit 10;
|
|
|
relname | buffered | buffer_percent | percent_of_relation
|
|
|
--------------+------------+----------------+---------------------
|
|
|
test_tbl | 18 MB | 0.3 | 0.2
|
|
|
pg_am | 8192 bytes | 0.0 | 20.0
|
|
|
pg_index | 24 kB | 0.0 | 37.5
|
|
|
pg_amproc | 32 kB | 0.0 | 50.0
|
|
|
pg_cast | 16 kB | 0.0 | 33.3
|
|
|
pg_depend | 64 kB | 0.0 | 13.3
|
|
|
pg_amop | 48 kB | 0.0 | 54.5
|
|
|
pg_namespace | 8192 bytes | 0.0 | 20.0
|
|
|
pg_opclass | 16 kB | 0.0 | 28.6
|
|
|
pg_aggregate | 8192 bytes | 0.0 | 16.7
|
|
|
(10 rows)
|
|
|
|
|
|
Time: 163.936 ms
|
|
|
test=#
|
|
|
</code></pre>
|
|
|
|
|
|
<p>強制把test_tbl 全部塞進 shared_buffers</p>
|
|
|
|
|
|
<pre><code>test=# select pg_prewarm('test_tbl','buffer');
|
|
|
pg_prewarm
|
|
|
------------
|
|
|
1327434
|
|
|
(1 row)
|
|
|
|
|
|
Time: 7472.805 ms (00:07.473)
|
|
|
test=#
|
|
|
</code></pre>
|
|
|
|
|
|
<p>確認一下test_tbl 有沒有被整個塞進去</p>
|
|
|
|
|
|
<pre><code>test=# select c.relname,pg_size_pretty(count(*) * 8192) as buffered,
|
|
|
round(100.0 * count(*) / (
|
|
|
select setting from pg_settings
|
|
|
where name='shared_buffers')::integer,1)
|
|
|
as buffer_percent,
|
|
|
round(100.0*count(*)*8192 / pg_table_size(c.oid),1) as percent_of_relation
|
|
|
from pg_class c inner join pg_buffercache b on b.relfilenode = c.relfilenode inner
|
|
|
join pg_database d on ( b.reldatabase =d.oid and d.datname =current_database())
|
|
|
group by c.oid,c.relname order by 3 desc limit 10;
|
|
|
relname | buffered | buffer_percent | percent_of_relation
|
|
|
--------------+------------+----------------+---------------------
|
|
|
test_tbl | 6142 MB | 100.0 | 59.2
|
|
|
pg_am | 8192 bytes | 0.0 | 20.0
|
|
|
pg_index | 24 kB | 0.0 | 37.5
|
|
|
pg_amproc | 32 kB | 0.0 | 50.0
|
|
|
pg_cast | 16 kB | 0.0 | 33.3
|
|
|
pg_depend | 24 kB | 0.0 | 5.0
|
|
|
pg_amop | 40 kB | 0.0 | 45.5
|
|
|
pg_namespace | 8192 bytes | 0.0 | 20.0
|
|
|
pg_opclass | 16 kB | 0.0 | 28.6
|
|
|
pg_aggregate | 8192 bytes | 0.0 | 16.7
|
|
|
(10 rows)
|
|
|
|
|
|
Time: 4985.366 ms (00:04.985)
|
|
|
test=#
|
|
|
</code></pre>
|
|
|
|
|
|
<p>GOOD ！ let’s do explain again !</p>
|
|
|
|
|
|
<pre><code>test=# explain (analyze,buffers) select count(*) from test_tbl;
|
|
|
Time: 11451.188 ms (00:11.451)
|
|
|
QUERY PLAN
|
|
|
--------------------------------------------------------------------------------------------------------------------
|
|
|
Finalize Aggregate (cost=2265934.72..2265934.73 rows=1 width=8) (actual time=11231.664..11231.664 rows=1 loops=1)
|
|
|
Buffers: shared hit=785963 read=541471
|
|
|
-> Gather (cost=2265934.30..2265934.71 rows=4 width=8) (actual time=11231.606..11450.719 rows=5 loops=1)
|
|
|
Workers Planned: 4
|
|
|
Workers Launched: 4
|
|
|
Buffers: shared hit=785963 read=541471
|
|
|
-> Partial Aggregate (cost=2264934.30..2264934.31 rows=1 width=8) (actual time=11228.829..11228.830 rows=1 loops=5)
|
|
|
Buffers: shared hit=785963 read=541471
|
|
|
-> Parallel Seq Scan on test_tbl (cost=0.00..2077434.24 rows=75000024 width=0) (actual time=0.037..6414.711 rows=60000000 loops=5)
|
|
|
Buffers: shared hit=785963 read=541471
|
|
|
Planning Time: 0.039 ms
|
|
|
Execution Time: 11450.781 ms
|
|
|
(12 rows)
|
|
|
</code></pre>
|
|
|
|
|
|
<p>確認一下，果然大部分都打到cache 了，但是因為shared_buffers 不夠大，所以還會從磁碟讀取一部分</p>
|
|
|
|
|
|
<p>而且時間也比之前還沒塞進shared_buffers 的時候要快了不少</p>
|
|
|
|
|
|
<p>22908.571 –> 11450.781 ms</p>
|
|
|
|
|
|
<hr />
|
|
|
|
|
|
<p>從這次的測試看來，我想如果有足夠大的記憶體，能夠把資料表都塞入shared_buffers 中</p>
|
|
|
|
|
|
<p>應該可以帶來不錯的效能增幅！</p>
|
|
|
</article>
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</div>
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<a href="/categories/%E7%AD%86%E8%A8%98" title="View all posts in 筆記">筆記</a>
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<div class="entry-tags"><p><span>Tags</span>
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<a href="/tags/postgresql" title="View all posts tagged postgresql">postgresql</a>
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</p></div> </div>
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<div class="author-meta">
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<div class="author">
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<img alt='Eric Chang' src="https://www.gravatar.com/avatar/23f8ed94e007297499ac8df1641b3ff5?s=100&d=identicon" class='avatar avatar-72 photo' height='72' width='72'>
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<span>
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Written by:<a href="https://github.com/changchichung" title="Posts by Eric Chang" rel="author">Eric Chang</a> </span>
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<div class="bio">
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<p>塵世裡一個迷途小書僮</p>
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</ul> <div class="design-credit">
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