GSoC 2015 proposal: Support for microvacuum for GiST

Hi, hackers!

I want to show my proposal idea for GSoC 2015. I'm newbie to coding for
PostgreSQL.

http://www.google-melange.com/gsoc/proposal/public/google/gsoc2015/ivanitskiy_ilya/5629499534213120

***
*Abstract:*
Currently support for microvacuum is implemented only for BTree index. But
GiST index is so useful and widely used for user defined datatypes instead
of btree. During index search it reads page by page. Every tuple on the
page in buffer marked as "dead" if it doesn't visible for all transactions.
Whenever before receiving next page we check "dead" items and mark current
page as "has garbage"[1]. When the page gets full, all the killed items are
removed by calling microvacuum[2].

*Benefits **to **the **PostgreSQL **Community*

The improvement can reduce handover time during execution VACUUM. It will
be useful for high-loaded system, where PostgreSQL is used.

*Quantifiable results*

Reducing VACUUM run time and INSERT run time for GiST.

*Project **details *

I'm going to implement support for microvacuum for GiST as well as it was
implemented for BTree access method, just taking into account specificity
of GiST.

During IndexScan we get pages from GiST index and download elected page one
by one into buffer. Every item from buffering page is checked for "dead".
If item really is "dead", we write item's adress in structure BTScanOpaque
<http://doxygen.postgresql.org/structBTScanOpaqueData.html> in function
btgettuple(). Before receiving next pafe into buffer it is started
_bt_killitems()
<http://doxygen.postgresql.org/nbtutils_8c.html#a60f25ce314f5395e6f6ae44ccbae8859>,
which checked "dead" tuples with function ItemPointerEquals
<http://doxygen.postgresql.org/itemptr_8c.html#ad919b8efe8c466023017a83955157d6b>
(). If page contains at least one "dead" tuple, it's marked:
opaque->btpo_flags |= BTP_HAS_GARBAGE
<http://doxygen.postgresql.org/nbtree_8h.html#a3b7c77849276ff8617edc1f84441c230>
;
MarkBufferDirtyHint
<http://doxygen.postgresql.org/bufmgr_8c.html#ac40bc4868e97a49a25dd8be7c98b6773>
(so->currPos
<http://doxygen.postgresql.org/structBTScanOpaqueData.html#a70a715bd5c5db16b699f5449495b0f70>
.buf
<http://doxygen.postgresql.org/structBTScanPosData.html#a26f8687a5a566266e4d4190a4c16a0ef>,
true);

_bt_killitems()
<http://doxygen.postgresql.org/nbtutils_8c.html#a60f25ce314f5395e6f6ae44ccbae8859>
is
called when we want to download next page to buffer or end of IndexScan or
ReScan.

Further, when call chain is called btinsert() -> _bt_doinsert() ->
_bt_findinsertloc(), if the page, which should be carried out insert, is
marked by HAS_GARBAGE flag, then function _bt_vacuum_one_page() is started.
It vacuum just one index page.

I'm going to realize such features for GiST index.

*Project Schedule *

until May 31

Solve architecture questions with help of community.

1 June – 30 June

First, approximate implementation supporting microvacuum for GiST.

I’ve got bachelor's degree in this month so I haven’t much time to work on
project.

1 July – 31 July

Implementation of supporting microvacuum for GiST and testing.

1 August -15 August

Final refactoring, testing and committing.

*About myself*

I'm last year student at Moscow Engineering and Physical Institute at
department "Cybernetics".

*Links *

1.
http://doxygen.postgresql.org/nbtutils_8c.html#a60f25ce314f5395e6f6ae44ccbae8859
2.
http://doxygen.postgresql.org/nbtinsert_8c.html#a89450d93d20d3d5e2d1e68849b69ee32
3. https://wiki.postgresql.org/wiki/GSoC_2015#Core

_______________________________________________________________________________

Best wishes,

Ivanitskiy Ilya.
<https://slovari.yandex.ru/newbie/en-ru>