Using CURSOR_SPACE_FOR_TIME

本文探讨了通过调整CURSOR_SPACE_FOR_TIME参数来优化Oracle数据库中SQL语句执行性能的方法。该参数控制是否允许为节省内存而从库缓存中移除游标。设置为true可以略微提升执行速度,但需确保共享池足够大以避免错误。

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If you have no library cache misses, then you might be able to accelerate execution calls by setting the value of the initialization parameter CURSOR_SPACE_FOR_TIME to true. This parameter specifies whether a cursor can be deallocated from the library cache to make room for a new SQL statement. CURSOR_SPACE_FOR_TIME has the following values meanings:

  • If CURSOR_SPACE_FOR_TIME is set to false (the default), then a cursor can be deallocated from the library cache regardless of whether application cursors associated with its SQL statement are open. In this case, Oracle must verify that the cursor containing the SQL statement is in the library cache.
  • If CURSOR_SPACE_FOR_TIME is set to true, then a cursor can be deallocated only when all application cursors associated with its statement are closed. In this case, Oracle need not verify that a cursor is in the cache, because it cannot be deallocated while an application cursor associated with it is open.

Setting the value of the parameter to true saves Oracle a small amount of time and can slightly improve the performance of execution calls. This value also prevents the deallocation of cursors until associated application cursors are closed.

Do not set the value of CURSOR_SPACE_FOR_TIME to true if you have found library cache misses on execution calls. Such library cache misses indicate that the shared pool is not large enough to hold the shared SQL areas of all concurrently open cursors. If the value is true, and if the shared pool has no space for a new SQL statement, then the statement cannot be parsed, and Oracle returns an error saying that there is no more shared memory. If the value is false, and if there is no space for a new statement, then Oracle deallocates an existing cursor. Although deallocating a cursor could result in a library cache miss later (only if the cursor is reexecuted), it is preferable to an error halting your application because a SQL statement cannot be parsed.

Do not set the value of CURSOR_SPACE_FOR_TIME to true if the amount of memory available to each user for private SQL areas is scarce. This value also prevents the deallocation of private SQL areas associated with open cursors. If the private SQL areas for all concurrently open cursors fills your available memory so that there is no space for a new SQL statement, then the statement cannot be parsed. Oracle returns an error indicating that there is not enough memory.

 

详细分析解释一下chromium源码中的下面的函数: class OmniboxViewViews : public OmniboxView, public views::Textfield, #if BUILDFLAG(IS_CHROMEOS) public ash::input_method::InputMethodManager::CandidateWindowObserver, #endif public views::TextfieldController, public ui::CompositorObserver, public TemplateURLServiceObserver { METADATA_HEADER(OmniboxViewViews, views::Textfield) public: // Max width of the gradient mask used to smooth ElideAnimation edges. static const int kSmoothingGradientMaxWidth = 15; OmniboxViewViews(std::unique_ptr<OmniboxClient> client, bool popup_window_mode, LocationBarView* location_bar_view, const gfx::FontList& font_list); OmniboxViewViews(const OmniboxViewViews&) = delete; OmniboxViewViews& operator=(const OmniboxViewViews&) = delete; ~OmniboxViewViews() override; // Initialize, create the underlying views, etc. void Init(); // Exposes the RenderText for tests. #if defined(UNIT_TEST) gfx::RenderText* GetRenderText() { return views::Textfield::GetRenderText(); } #endif // For use when switching tabs, this saves the current state onto the tab so // that it can be restored during a later call to Update(). void SaveStateToTab(content::WebContents* tab); // Called when the window's active tab changes. void OnTabChanged(const content::WebContents* web_contents); // Called to clear the saved state for |web_contents|. void ResetTabState(content::WebContents* web_contents); // Installs the placeholder text with the name of the current default search // provider. For example, if Google is the default search provider, this shows // "Search Google or type a URL" when the Omnibox is empty and unfocused. void InstallPlaceholderText(); // Indicates if the cursor is at the end of the input. Requires that both // ends of the selection reside there. bool GetSelectionAtEnd() const; // Returns the width in pixels needed to display the current text. The // returned value includes margins. int GetTextWidth() const; // Returns the width in pixels needed to display the current text unelided. int GetUnelidedTextWidth() const; // Returns the omnibox's width in pixels. int GetWidth() const; // OmniboxView: void EmphasizeURLComponents() override; void Update() override; std::u16string GetText() const override; using OmniboxView::SetUserText; void SetUserText(const std::u16string& text, bool update_popup) override; void SetWindowTextAndCaretPos(const std::u16string& text, size_t caret_pos, bool update_popup, bool notify_text_changed) override; void SetAdditionalText(const std::u16string& additional_text) override; void EnterKeywordModeForDefaultSearchProvider() override; bool IsSelectAll() const override; void GetSelectionBounds(std::u16string::size_type* start, std::u16string::size_type* end) const override; void SelectAll(bool reversed) override; void RevertAll() override; void SetFocus(bool is_user_initiated) override; bool IsImeComposing() const override; gfx::NativeView GetRelativeWindowForPopup() const override; bool IsImeShowingPopup() const override; // views::Textfield: gfx::Size GetMinimumSize() const override; bool OnMousePressed(const ui::MouseEvent& event) override; bool OnMouseDragged(const ui::MouseEvent& event) override; void OnMouseReleased(const ui::MouseEvent& event) override; void OnPaint(gfx::Canvas* canvas) override; void ExecuteCommand(int command_id, int event_flags) override; void OnInputMethodChanged() override; void AddedToWidget() override; void RemovedFromWidget() override; std::u16string GetLabelForCommandId(int command_id) const override; bool IsCommandIdEnabled(int command_id) const override; // For testing only. OmniboxPopupView* GetPopupViewForTesting() const; protected: // OmniboxView: void UpdateSchemeStyle(const gfx::Range& range) override; // views::Textfield: void OnThemeChanged() override; bool IsDropCursorForInsertion() const override; // Wrappers around Textfield methods that tests can override. virtual void ApplyColor(SkColor color, const gfx::Range& range); virtual void ApplyStyle(gfx::TextStyle style, bool value, const gfx::Range& range); private: friend class TestingOmniboxView; FRIEND_TEST_ALL_PREFIXES(OmniboxPopupViewViewsTest, EmitAccessibilityEvents); // TODO(tommycli): Remove the rest of these friends after porting these // browser tests to unit tests. FRIEND_TEST_ALL_PREFIXES(OmniboxViewViewsTest, CloseOmniboxPopupOnTextDrag); FRIEND_TEST_ALL_PREFIXES(OmniboxViewViewsTest, FriendlyAccessibleLabel); FRIEND_TEST_ALL_PREFIXES(OmniboxViewViewsTest, DoNotNavigateOnDrop); FRIEND_TEST_ALL_PREFIXES(OmniboxViewViewsTest, AyncDropCallback); FRIEND_TEST_ALL_PREFIXES(OmniboxViewViewsTest, AccessibleTextSelectBoundTest); enum class UnelisionGesture { HOME_KEY_PRESSED, MOUSE_RELEASE, OTHER, }; // Update the field with |text| and set the selection. |ranges| should not be // empty; even text with no selections must have at least 1 empty range in // |ranges| to indicate the cursor position. void SetTextAndSelectedRange(const std::u16string& text, const gfx::Range& selection); // Returns the selected text. std::u16string_view GetSelectedText() const; void UpdateAccessibleTextSelection() override; // Paste text from the clipboard into the omnibox. // Textfields implementation of Paste() pastes the contents of the clipboard // as is. We want to strip whitespace and other things (see GetClipboardText() // for details). The function invokes OnBefore/AfterPossibleChange() as // necessary. void OnOmniboxPaste(); // Handle keyword hint tab-to-search and tabbing through dropdown results. bool HandleEarlyTabActions(const ui::KeyEvent& event); void ClearAccessibilityLabel(); void SetAccessibilityLabel(const std::u16string& display_text, const AutocompleteMatch& match, bool notify_text_changed) override; // Returns true if the user text was updated with the full URL (without // steady-state elisions). |gesture| is the user gesture causing unelision. bool UnapplySteadyStateElisions(UnelisionGesture gesture); #if BUILDFLAG(IS_MAC) void AnnounceFriendlySuggestionText(); #endif // Get the preferred text input type, this checks the IME locale on Windows. ui::TextInputType GetPreferredTextInputType() const; // OmniboxView: void SetCaretPos(size_t caret_pos) override; void UpdatePopup() override; void ApplyCaretVisibility() override; void OnTemporaryTextMaybeChanged(const std::u16string& display_text, const AutocompleteMatch& match, bool save_original_selection, bool notify_text_changed) override; void OnInlineAutocompleteTextMaybeChanged( const std::u16string& user_text, const std::u16string& inline_autocompletion) override; void OnInlineAutocompleteTextCleared() override; void OnRevertTemporaryText(const std::u16string& display_text, const AutocompleteMatch& match) override; void OnBeforePossibleChange() override; bool OnAfterPossibleChange(bool allow_keyword_ui_change) override; void OnKeywordPlaceholderTextChange() override; gfx::NativeView GetNativeView() const override; void ShowVirtualKeyboardIfEnabled() override; void HideImeIfNeeded() override; int GetOmniboxTextLength() const override; void SetEmphasis(bool emphasize, const gfx::Range& range) override; // views::View void OnMouseMoved(const ui::MouseEvent& event) override; void OnMouseExited(const ui::MouseEvent& event) override; // views::Textfield: bool IsItemForCommandIdDynamic(int command_id) const override; void OnGestureEvent(ui::GestureEvent* event) override; bool SkipDefaultKeyEventProcessing(const ui::KeyEvent& event) override; bool HandleAccessibleAction(const ui::AXActionData& action_data) override; void OnFocus() override; void OnBlur() override; std::u16string GetSelectionClipboardText() const override; void DoInsertChar(char16_t ch) override; bool IsTextEditCommandEnabled(ui::TextEditCommand command) const override; void ExecuteTextEditCommand(ui::TextEditCommand command) override; bool ShouldShowPlaceholderText() const override; void UpdateAccessibleValue() override; // ash::input_method::InputMethodManager::CandidateWindowObserver: #if BUILDFLAG(IS_CHROMEOS) void CandidateWindowOpened( ash::input_method::InputMethodManager* manager) override; void CandidateWindowClosed( ash::input_method::InputMethodManager* manager) override; #endif // views::TextfieldController: void ContentsChanged(views::Textfield* sender, const std::u16string& new_contents) override; bool HandleKeyEvent(views::Textfield* sender, const ui::KeyEvent& key_event) override; void OnBeforeUserAction(views::Textfield* sender) override; void OnAfterUserAction(views::Textfield* sender) override; void OnAfterCutOrCopy(ui::ClipboardBuffer clipboard_buffer) override; void OnWriteDragData(ui::OSExchangeData* data) override; void OnGetDragOperationsForTextfield(int* drag_operations) override; void AppendDropFormats( int* formats, std::set<ui::ClipboardFormatType>* format_types) override; ui::mojom::DragOperation OnDrop(const ui::DropTargetEvent& event) override; views::View::DropCallback CreateDropCallback( const ui::DropTargetEvent& event) override; void UpdateContextMenu(ui::SimpleMenuModel* menu_contents) override; // ui::SimpleMenuModel::Delegate: bool IsCommandIdChecked(int id) const override; // ui::CompositorObserver: void OnCompositingDidCommit(ui::Compositor* compositor) override; void OnCompositingStarted(ui::Compositor* compositor, base::TimeTicks start_time) override; void OnDidPresentCompositorFrame( uint32_t frame_token, const gfx::PresentationFeedback& feedback) override; void OnCompositingShuttingDown(ui::Compositor* compositor) override; // TemplateURLServiceObserver: void OnTemplateURLServiceChanged() override; // Permits launch of the external protocol handler after user actions in // the omnibox. The handler needs to be informed that omnibox input should // always be considered "user gesture-triggered", lest it always return BLOCK. void PermitExternalProtocolHandler(); // Drops dragged text and updates `output_drag_op` accordingly. void PerformDrop(const ui::DropTargetEvent& event, ui::mojom::DragOperation& output_drag_op, std::unique_ptr<ui::LayerTreeOwner> drag_image_layer_owner); // Helper method to construct part of the context menu. void MaybeAddSendTabToSelfItem(ui::SimpleMenuModel* menu_contents); // Called when the popup view becomes visible. void OnPopupOpened(); // Helper for updating placeholder color depending on whether its a keyword or // DSE placeholder. void UpdatePlaceholderTextColor(); // When true, the location bar view is read only and also is has a slightly // different presentation (smaller font size). This is used for popups. bool popup_window_mode_; // Owns either an OmniboxPopupViewViews or an OmniboxPopupViewWebUI. std::unique_ptr<OmniboxPopupView> popup_view_; base::CallbackListSubscription popup_view_opened_subscription_; // Selection persisted across temporary text changes, like popup suggestions. gfx::Range saved_temporary_selection_; // Holds the user's selection across focus changes. There is only a saved // selection if this range IsValid(). gfx::Range saved_selection_for_focus_change_; // Tracking state before and after a possible change. State state_before_change_; bool ime_composing_before_change_ = false; // |location_bar_view_| can be NULL in tests. raw_ptr<LocationBarView> location_bar_view_; #if BUILDFLAG(IS_CHROMEOS) // True if the IME candidate window is open. When this is true, we want to // avoid showing the popup. So far, the candidate window is detected only // on Chrome OS. bool ime_candidate_window_open_ = false; #endif // True if any mouse button is currently depressed. bool is_mouse_pressed_ = false; // Applies a minimum threshold to drag events after unelision. Because the // text shifts after unelision, we don't want unintentional mouse drags to // change the selection. bool filter_drag_events_for_unelision_ = false; // Should we select all the text when we see the mouse button get released? // We select in response to a click that focuses the omnibox, but we defer // until release, setting this variable back to false if we saw a drag, to // allow the user to select just a portion of the text. bool select_all_on_mouse_release_ = false; // Indicates if we want to select all text in the omnibox when we get a // GESTURE_TAP. We want to select all only when the textfield is not in focus // and gets a tap. So we use this variable to remember focus state before tap. bool select_all_on_gesture_tap_ = false; // Whether the user should be notified if the clipboard is restricted. bool show_rejection_ui_if_any_ = false; // Keep track of the word that would be selected if URL is unelided between // a single and double click. This is an edge case where the elided URL is // selected. On the double click, unelision is performed in between the first // and second clicks. This results in both the wrong word to be selected and // the wrong selection length. For example, if example.com is shown and you // try to double click on the "x", it unelides to https://example.com after // the first click, resulting in "https" being selected. size_t next_double_click_selection_len_ = 0; size_t next_double_click_selection_offset_ = 0; // The time of the first character insert operation that has not yet been // painted. Used to measure omnibox responsiveness with a histogram. base::TimeTicks insert_char_time_; // The state machine for logging the Omnibox.CharTypedToRepaintLatency // histogram. enum { NOT_ACTIVE, // Not currently tracking a char typed event. CHAR_TYPED, // Character was typed. ON_PAINT_CALLED, // Character was typed and OnPaint() called. COMPOSITING_COMMIT, // Compositing was committed after OnPaint(). COMPOSITING_STARTED, // Compositing was started. } latency_histogram_state_; // The currently selected match, if any, with additional labelling text // such as the document title and the type of search, for example: // "Google https://google.com location from bookmark", or // "cats are liquid search suggestion". std::u16string friendly_suggestion_text_; // The number of added labelling characters before editable text begins. // For example, "Google https://google.com location from history", // this is set to 7 (the length of "Google "). int friendly_suggestion_text_prefix_length_; base::ScopedObservation<ui::Compositor, ui::CompositorObserver> scoped_compositor_observation_{this}; base::ScopedObservation<TemplateURLService, TemplateURLServiceObserver> scoped_template_url_service_observation_{this}; PrefChangeRegistrar pref_change_registrar_; base::WeakPtrFactory<OmniboxViewViews> weak_factory_{this}; };
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