Drop Down MenusCSS Drop Down MenuPure CSS Dropdown Menu

Postgresql Increase Performance Query (Sequential scan) Without Index -understanding For Cache Memory

-
  • A sequential scan i.e when there is no index and postgres has to fetch all the data from disk are a problem area for a cache like this.
  • Since a single seq scan can wipe all of the data from a cache, it is handled differently.
  • Instead of using a normal LRU/clock sweep algorithm, it uses a series of buffers of total 256 K.B in size. The below plan shows how it is handled.
test=# explain (analyze,buffers) select count(*) from emp;
   
  Aggregate  (cost=48214.95..48214.96 rows=1 width=0) (actual time=3874.445..3874.445 rows=1 loops=1)
    Buffers: shared read=35715
    ->  Seq Scan on emp  (cost=0.00..45714.96 rows=999996 width=0) (actual time=6.024..3526.606 rows=1000000 loops=1)
          Buffers: shared read=35715
  Planning time: 0.114 ms
  Execution time: 3874.509 ms

Executing the above query again.

test=# explain (analyze,buffers) select count(*) from emp;
      Aggregate  (cost=48214.95..48214.96 rows=1 width=0) (actual time=426.385..426.385 rows=1 loops=1)
    Buffers: shared hit=32 read=35683
    ->  Seq Scan on emp  (cost=0.00..45714.96 rows=999996 width=0) (actual time=0.036..285.363 rows=1000000 loops=1)
          Buffers: shared hit=32 read=35683
  Planning time: 0.048 ms
  Execution time: 426.431 ms
We can see that exactly 32 blocks have moved into memory i.e 32 * 8 = 256 KB.

Comments

Post a Comment

Popular posts from this blog

VMWARE WORKSTATION 3,4,5,6,7,8,9,10,11,12,14,15...etc LICENSE KEYS COLLECTION

-
Image
Below tutorialdba.com collected and sorted out hundreds of universal License Keys for all major versions of VMware Workstation Pro (not for VMware Workstation Player) 4.x, 5.x, 6.x, 7.x, 8.x, 9.x, 10.x, 11.x, 12.x and v14.x on Windows and Linux platforms (support both 32-bit and 64-bit operating system) in this single post. Besides, we also provide some license keys for VMware other projects. Just enjoy and share them. // 4~14 Universal License Keys // Version License Keys VMware Workstation VMware Workstation 4.x.x ZHDH1-UR90N-W844G-4PTN6 G1NP0-T88AL-M016F-4P8N2 ZC14J-4U16A-0A04G-4MEZP J1WF8-58LDE-881DG-4M8Q3 VMware Workstation 5.x.x LUXRM-WP0DN-A256U-4M9Q3 DJXDR-NDT27-Y2NDU-4YTZK DA925-HP80U-Z8HDC-4WXXP 3KW2W-AYR2C-88M6F-4MDQ2 VMware Workstation 6.x.x A0E8R-YUDFV-6AK2F-4GAN2 CRX0D-VWL0V-7CJ6C-46C7A NA8RX-QPNDU-D2LA9-4WAZL 1H4WM-N21FZ-7GK2A-44U5U 6AJ6N-THY2P-42KEF-4WTFG FK8R9-LPCDT-88H4Y-4WRN3 KAR8R-T8MAL-K8J6A-4WDXQ YJEKW-JMFF4-YA1DC-4WTQ...
Read more

Postgres Database Patch

-
If you are used to patch Oracle databases you probably know how to use opatch to apply PSUs. How does PostgreSQL handle this? Do we need to patch the existing binaries to apply security fixes? The answer is: No.Lets say you want to patch PostgreSQL from version 10.5/11.3 to version 10.10/11.5. This is called minor version postgres upgrade or postgres patching Why need to patch postgresql server  ? Multiple SQL injection vulnerabilities have been discovered in PostgreSQL that could allow for arbitrary code execution. The vulnerabilities are the result of the application’s failure to sufficiently sanitize user-supplied input before using it in an SQL query. These vulnerabilities allow attackers with the CREATE permission (or Trigger permission in some tables) to exploit input sanitation vulnerabilities in the pg_upgrade and pg_dump functions. The CREATE permission is automatically given to new users on the public schema, and the public schema is the default schema used on the...
Read more

How to find the server is whether standby (slave) or primary(master) in Postgresql replication ?

-
Method 1 You can check the mode of the server using "pg_controldata". [pgsql@test~]$ pg_controldata /usr/local/pgsql/data84/ Database cluster state: in archive recovery --> This is Standby Database Database cluster state: in production --> This is Production Database [Master] Method 2 You can use pg_is_in_recovery() which returns True if recovery is still in progress(so the server is running in standby mode or slave) postgres=# select pg_is_in_recovery(); pg_is_in_recovery ------------------- t (1 row) If Return    false   so the server is running in primary mode or master postgres=# select pg_is_in_recovery(); pg_is_in_recovery ------------------- f (1 row)
Read more

How to Enable/Disable autovacuum on PostgreSQL

-
Introduced in PostgreSQL 8.1, the AUTOVACUUM daemon is an optional feature that automatically vacuums the database so that you don't have to manually run the  VACUUM statement . The AUTOVACUUM daemon is enabled in the default configuration. The AUTOVACUUM daemon is made up of multiple processes that reclaim storage by removing obsolete data or tuples from the database. It checks for tables that have a significant number of inserted, updated, or deleted records and vacuums these tables based on the configuration settings below. Default Settings The AUTOVACUUM settings for PostgreSQL can be found in the  postgresql.conf  file and control when/how the daemon runs. The following is an example of these settings: #------------------------------------------------------------------------------ # AUTOVACUUM PARAMETERS #------------------------------------------------------------------------------ autovacuum = on # Enable autovacuum subprocess? ...
Read more

PostgreSQL Enterprise Manager - PEM Monitoring Tools

-
Image
Database administration and management is required for any database on which there are continuous business transactions.  If databases across enterprises are not monitored and maintained, then such databases are vulnerable to disasters, which eventually brings downtime to missions-critical application and, of course, it will incur losses in the business. Data is now one of the key assets for running a business, globally. Hence, it is one of the major responsibilities of enterprises to invest in resources for database monitoring and management. There are many database management and monitoring tools available for proactive database monitoring. In this article, we will look at  PEM – “PostgreSQL Enterprise Manager” .Enterprise Manager, or PEM, is a graphical database management/monitoring tool that can help database administrators, system administrators, database developers, database managers, system architects, and performance analysts manage databases efficiently and proacti...
Read more