Horton

Re: [Proposal] Global temporary tables

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: wenjing@gmail.com
Cc: shawn wang <shawn.wang.pg@gmail.com>, Pavel Stehule <pavel.stehule@gmail.com>, Andrew Dunstan <andrew@dunslane.net>, 曾文旌 <wenjing.zwj@alibaba-inc.com>, Robert Haas <robertmhaas@gmail.com>, Prabhat Sahu <prabhat.sahu@enterprisedb.com>, tushar <tushar.ahuja@enterprisedb.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2021-05-10T10:43:53Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. PageAddItemExtended(): Add LP_UNUSED assertion.

  2. Remove temporary files after backend crash

  3. Fix comment in indexing.c

  4. Fix failure to ignore leftover temp tables after a server crash.

On Thu, Apr 22, 2021 at 1:11 PM wenjing <wjzeng2012@gmail.com> wrote:
>

I have briefly looked into the design comments added by the patch.  I
have a few questions.

+Feature description
+--------------------------------
+
+Previously, temporary tables are defined once and automatically
+created (starting with empty contents) in every session before using them.


I don’t think this statement is correct, I mean if we define a temp
table in one session then it doesn’t automatically create in all the
sessions.


+
+Like local temporary table, Global Temporary Table supports ON COMMIT
PRESERVE ROWS
+or ON COMMIT DELETE ROWS clause, so that data in the temporary table can be
+cleaned up or reserved automatically when a session exits or a
transaction COMMITs.

/reserved/preserved


I was trying to look into the “Main design idea” section.

+1) CATALOG
+GTTs store session-specific data. The storage information of GTTs'data, their
+transaction information, and their statistics are not stored in the catalog.

I did not understand what do you mean by “transaction information” is
not stored in the catalog?  Mean what transaction information are
stored in catalog in the normal table which is not stored for GTT?

+Changes to the GTT's metadata affect all sessions.
+The operations making those changes include truncate GTT, Vacuum/Cluster GTT,
+and Lock GTT.

How does Truncate or Vacuum affect all the sessions, I mean truncate
should only truncate the data of the current session and the same is
true for the vacuum no?

I will try to do a more detailed review.

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com