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Date: Fri, 6 Jul 2007 02:28:04 -0700 (PDT)
From: "Knut Anders Hatlen (JIRA)" <jira@apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Updated: (DERBY-2878) Scan protection handle could be cached
 in BasePage
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     [ https://issues.apache.org/jira/browse/DERBY-2878?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Knut Anders Hatlen updated DERBY-2878:
--------------------------------------

    Attachment: derby-2878-3.stat
                derby-2878-3.diff

Attaching a new patch which removes the allocation of a scan
protection handle when the scan is unlocked. This removes one RecordId
allocation and one PageKey allocation per visited leaf node in a
B-tree scan.

What the patch does, is

  1) Remove the current_scan_pageno field from BTreeRowPosition and
  replace it with current_scan_protectionHandle (a RecordHandle).

  2) Change the signature of unlockScan() so that it takes a record
  handle instead of a page number.

  3) Add a method isRowLockingPolicy() to the BTreeLockingPolicy
  interface. This method returns false for the B2INoLocking classes
  and true for the B2IRowLocking classes. The return value is used to
  determine whether a protection handle should be requested.

  4) Where the B-tree scan previously set current_scan_pageno to the
  page number, now set current_scan_protectionHandle to the scan
  protection record handle if isRowLockingPolicy() returns true. This
  code has also been factored out into a separate method called
  BTreeScan.setCurrentScanProtectionHandle().

  5) Remove OpenBTree.makeRecordHandle() which is no longer used.

  6) Change all the asserts that used current_scan_pageno so that they
  use current_scan_protectionHandle.

All the regression tests (derbyall and suites.All) passed.

> Scan protection handle could be cached in BasePage
> --------------------------------------------------
>
>                 Key: DERBY-2878
>                 URL: https://issues.apache.org/jira/browse/DERBY-2878
>             Project: Derby
>          Issue Type: Improvement
>          Components: Performance, Store
>    Affects Versions: 10.4.0.0
>            Reporter: Knut Anders Hatlen
>            Assignee: Knut Anders Hatlen
>            Priority: Minor
>         Attachments: derby-2878-1.diff, derby-2878-1.stat, derby-2878-1b.diff, derby-2878-2.diff, derby-2878-3.diff, derby-2878-3.stat
>
>
> Each time a leaf node in a B-tree is visited in an index scan, a scan protection row is locked and unlocked. Both the lock operation and the unlock operation will allocate a new RecordId object representing the scan protection row (the unlock operation additionally allocates a PageKey object for the RecordId). Since the scan protection handle created will be identical (seen from equals()) each time it is created for a page, it would make sense to cache it in BasePage. Then we only need to allocate the protection handle for a page once for as long as it stays in the page cache. This would save three object allocations per single-record lookup via index.

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