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feat: add CoW buffer for spring2024 p1 (#690)
* Prepare Spring 24 P1 * fix typo * add default impl for page guard constructor * format * new line at eof --------- Co-authored-by: xx01cyx <[email protected]>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,97 @@ | ||
| //===----------------------------------------------------------------------===// | ||
| // | ||
| // BusTub | ||
| // | ||
| // cow_buffer.h | ||
| // | ||
| // Identification: src/include/storage/disk/cow_buffer.h | ||
| // | ||
| // Copyright (c) 2015-2023, Carnegie Mellon University Database Group | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
|
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| #pragma once | ||
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| #include <cstdint> | ||
| #include <cstring> | ||
| #include "common/config.h" | ||
| #include "common/macros.h" | ||
| #include "storage/page/page.h" | ||
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| namespace bustub { | ||
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| /** | ||
| * CoWBuffer provides extra memory space other than the buffer pool to store the copy-on-write pages. | ||
| * It's purpose is to gather the copy of pages that are about to be written back to disk, so that the bpm | ||
| * doesn't have to incur IO penality and wait for the write to be completed when evicting. | ||
| * Spring 24: The buffer is limited to store a constant number of pages in total (8). | ||
| * !! ANY ATTEMPTS TO ADD ANOTHER IN-MEMORY CACHE WILL BE REVIEWED MANUALLY AS PER LEADERBOARD POLICY !! | ||
| */ | ||
| class CoWBuffer { | ||
| public: | ||
| CoWBuffer() : cow_pages_{new Page[8]} {} | ||
| ~CoWBuffer() { delete[] cow_pages_; } | ||
| DISALLOW_COPY_AND_MOVE(CoWBuffer); | ||
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| /** | ||
| * @brief Adds a new page to the CoW buffer. | ||
| * @param page the page pointer from the bpm that is about to be evicted. | ||
| * @return pointer to the copied page in the buffer, or nullptr if the buffer is full. | ||
| */ | ||
| auto Add(Page *page) -> Page * { | ||
| if ((page == nullptr) || IsFull()) { | ||
| return nullptr; | ||
| } | ||
|
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| uint32_t slot = FindFreeSlot(); | ||
| memcpy(cow_pages_[slot].GetData(), page->GetData(), BUSTUB_PAGE_SIZE); | ||
| MarkSlotUsed(slot); | ||
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| return cow_pages_ + slot; | ||
| } | ||
|
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| /** | ||
| * @brief Removes a page from the CoW buffer. | ||
| * @param page the pointer previously returned by Add. | ||
| */ | ||
| auto Remove(Page *page) -> void { | ||
| if (page != nullptr) { | ||
| MarkSlotFree(page - cow_pages_); | ||
| } | ||
| } | ||
|
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| private: | ||
| /** @brief Whether the buffer is full. */ | ||
| auto IsFull() -> bool { return free_slot_bitmap_ == 0xFFU; } | ||
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| /** @brief Finds a free slot in the buffer, if not full. */ | ||
| auto FindFreeSlot() -> uint32_t { | ||
| BUSTUB_ASSERT(!IsFull(), "no free slot in cow buffer"); | ||
| uint32_t i = 0; | ||
| uint8_t bitmap = free_slot_bitmap_; | ||
| while ((bitmap & 1U) != 0) { | ||
| bitmap >>= 1; | ||
| i++; | ||
| } | ||
| return i; | ||
| } | ||
|
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| /** @brief Marks a free slot as used. */ | ||
| void MarkSlotUsed(uint32_t slot) { | ||
| BUSTUB_ASSERT(((free_slot_bitmap_ >> slot) & 1U) == 0, "slot has already been used"); | ||
| free_slot_bitmap_ |= (1U << slot); | ||
| } | ||
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| /** @brief Marks a used slot as free. */ | ||
| void MarkSlotFree(uint32_t slot) { | ||
| BUSTUB_ASSERT(((free_slot_bitmap_ >> slot) & 1U) == 1, "slot is already free"); | ||
| free_slot_bitmap_ &= ~(1U << slot); | ||
| } | ||
|
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| /** The array of CoW buffer pages. */ | ||
| Page *cow_pages_; | ||
| /** The bitmap that records which slots are free. */ | ||
| uint8_t free_slot_bitmap_{0}; | ||
| }; | ||
|
|
||
| } // namespace bustub |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,55 @@ | ||
| //===----------------------------------------------------------------------===// | ||
| // | ||
| // BusTub | ||
| // | ||
| // page_guard_test.cpp | ||
| // | ||
| // Identification: test/storage/page_guard_test.cpp | ||
| // | ||
| // Copyright (c) 2015-2023, Carnegie Mellon University Database Group | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
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| #include "storage/disk/cow_buffer.h" | ||
| #include "gtest/gtest.h" | ||
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| namespace bustub { | ||
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| // NOLINTNEXTLINE | ||
| TEST(CoWBufferTest, ScheduleWriteReadPageTest) { | ||
| CoWBuffer cow{}; | ||
| std::vector<Page *> cow_pages{}; | ||
| for (size_t i{0}; i < 8; i++) { | ||
| Page bpm_page{}; | ||
| auto content{"Meuh!: " + std::to_string(i) + " 🐄🐄🐄🐄"}; | ||
| std::strncpy(bpm_page.GetData(), content.data(), BUSTUB_PAGE_SIZE); | ||
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| Page *cow_page{cow.Add(&bpm_page)}; | ||
| EXPECT_NE(cow_page, nullptr); | ||
| EXPECT_NE(cow_page, &bpm_page); | ||
| cow_pages.push_back(cow_page); | ||
| EXPECT_EQ(std::memcmp(cow_page->GetData(), bpm_page.GetData(), BUSTUB_PAGE_SIZE), 0); | ||
| } | ||
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| Page extra_page{}; | ||
| Page *cow_extra_page{cow.Add(&extra_page)}; | ||
| EXPECT_EQ(cow_extra_page, nullptr); | ||
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| for (size_t i{0}; i < 8; i++) { | ||
| auto check{"Meuh!: " + std::to_string(i) + " 🐄🐄🐄🐄"}; | ||
| EXPECT_EQ(std::memcmp(cow_pages[i]->GetData(), check.data(), check.size()), 0); | ||
| } | ||
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| cow.Remove(cow_pages[5]); | ||
| Page replace_page{}; | ||
| cow_pages[5] = cow.Add(&replace_page); | ||
| EXPECT_NE(cow_pages[5], nullptr); | ||
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| for (size_t i{0}; i < 8; i++) { | ||
| cow.Remove(cow_pages[i]); // Shouldn't crash. | ||
| } | ||
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| cow.Remove(nullptr); // Shouldn't crash. | ||
| } | ||
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| } // namespace bustub |