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0050a73a4f
Summary: This change standardizes on a new 16-byte cache key format for block cache (incl compressed and secondary) and persistent cache (but not table cache and row cache). The goal is a really fast cache key with practically ideal stability and uniqueness properties without external dependencies (e.g. from FileSystem). A fixed key size of 16 bytes should enable future optimizations to the concurrent hash table for block cache, which is a heavy CPU user / bottleneck, but there appears to be measurable performance improvement even with no changes to LRUCache. This change replaces a lot of disjointed and ugly code handling cache keys with calls to a simple, clean new internal API (cache_key.h). (Preserving the old cache key logic under an option would be very ugly and likely negate the performance gain of the new approach. Complete replacement carries some inherent risk, but I think that's acceptable with sufficient analysis and testing.) The scheme for encoding new cache keys is complicated but explained in cache_key.cc. Also: EndianSwapValue is moved to math.h to be next to other bit operations. (Explains some new include "math.h".) ReverseBits operation added and unit tests added to hash_test for both. Fixes https://github.com/facebook/rocksdb/issues/7405 (presuming a root cause) Pull Request resolved: https://github.com/facebook/rocksdb/pull/9126 Test Plan: ### Basic correctness Several tests needed updates to work with the new functionality, mostly because we are no longer relying on filesystem for stable cache keys so table builders & readers need more context info to agree on cache keys. This functionality is so core, a huge number of existing tests exercise the cache key functionality. ### Performance Create db with `TEST_TMPDIR=/dev/shm ./db_bench -bloom_bits=10 -benchmarks=fillrandom -num=3000000 -partition_index_and_filters` And test performance with `TEST_TMPDIR=/dev/shm ./db_bench -readonly -use_existing_db -bloom_bits=10 -benchmarks=readrandom -num=3000000 -duration=30 -cache_index_and_filter_blocks -cache_size=250000 -threads=4` using DEBUG_LEVEL=0 and simultaneous before & after runs. Before ops/sec, avg over 100 runs: 121924 After ops/sec, avg over 100 runs: 125385 (+2.8%) ### Collision probability I have built a tool, ./cache_bench -stress_cache_key to broadly simulate host-wide cache activity over many months, by making some pessimistic simplifying assumptions: * Every generated file has a cache entry for every byte offset in the file (contiguous range of cache keys) * All of every file is cached for its entire lifetime We use a simple table with skewed address assignment and replacement on address collision to simulate files coming & going, with quite a variance (super-Poisson) in ages. Some output with `./cache_bench -stress_cache_key -sck_keep_bits=40`: ``` Total cache or DBs size: 32TiB Writing 925.926 MiB/s or 76.2939TiB/day Multiply by 9.22337e+18 to correct for simulation losses (but still assume whole file cached) ``` These come from default settings of 2.5M files per day of 32 MB each, and `-sck_keep_bits=40` means that to represent a single file, we are only keeping 40 bits of the 128-bit cache key. With file size of 2\*\*25 contiguous keys (pessimistic), our simulation is about 2\*\*(128-40-25) or about 9 billion billion times more prone to collision than reality. More default assumptions, relatively pessimistic: * 100 DBs in same process (doesn't matter much) * Re-open DB in same process (new session ID related to old session ID) on average every 100 files generated * Restart process (all new session IDs unrelated to old) 24 times per day After enough data, we get a result at the end: ``` (keep 40 bits) 17 collisions after 2 x 90 days, est 10.5882 days between (9.76592e+19 corrected) ``` If we believe the (pessimistic) simulation and the mathematical generalization, we would need to run a billion machines all for 97 billion days to expect a cache key collision. To help verify that our generalization ("corrected") is robust, we can make our simulation more precise with `-sck_keep_bits=41` and `42`, which takes more running time to get enough data: ``` (keep 41 bits) 16 collisions after 4 x 90 days, est 22.5 days between (1.03763e+20 corrected) (keep 42 bits) 19 collisions after 10 x 90 days, est 47.3684 days between (1.09224e+20 corrected) ``` The generalized prediction still holds. With the `-sck_randomize` option, we can see that we are beating "random" cache keys (except offsets still non-randomized) by a modest amount (roughly 20x less collision prone than random), which should make us reasonably comfortable even in "degenerate" cases: ``` 197 collisions after 1 x 90 days, est 0.456853 days between (4.21372e+18 corrected) ``` I've run other tests to validate other conditions behave as expected, never behaving "worse than random" unless we start chopping off structured data. Reviewed By: zhichao-cao Differential Revision: D33171746 Pulled By: pdillinger fbshipit-source-id: f16a57e369ed37be5e7e33525ace848d0537c88f
293 lines
10 KiB
C++
293 lines
10 KiB
C++
#ifndef ROCKSDB_LITE
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#include "db/import_column_family_job.h"
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#include <algorithm>
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#include <cinttypes>
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#include <string>
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#include <vector>
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#include "db/version_edit.h"
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#include "file/file_util.h"
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#include "file/random_access_file_reader.h"
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#include "logging/logging.h"
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#include "table/merging_iterator.h"
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#include "table/scoped_arena_iterator.h"
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#include "table/sst_file_writer_collectors.h"
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#include "table/table_builder.h"
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#include "util/stop_watch.h"
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namespace ROCKSDB_NAMESPACE {
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Status ImportColumnFamilyJob::Prepare(uint64_t next_file_number,
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SuperVersion* sv) {
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Status status;
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// Read the information of files we are importing
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for (const auto& file_metadata : metadata_) {
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const auto file_path = file_metadata.db_path + "/" + file_metadata.name;
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IngestedFileInfo file_to_import;
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status =
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GetIngestedFileInfo(file_path, next_file_number++, &file_to_import, sv);
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if (!status.ok()) {
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return status;
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}
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files_to_import_.push_back(file_to_import);
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}
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auto num_files = files_to_import_.size();
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if (num_files == 0) {
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return Status::InvalidArgument("The list of files is empty");
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} else if (num_files > 1) {
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// Verify that passed files don't have overlapping ranges in any particular
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// level.
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int min_level = 1; // Check for overlaps in Level 1 and above.
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int max_level = -1;
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for (const auto& file_metadata : metadata_) {
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if (file_metadata.level > max_level) {
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max_level = file_metadata.level;
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}
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}
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for (int level = min_level; level <= max_level; ++level) {
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autovector<const IngestedFileInfo*> sorted_files;
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for (size_t i = 0; i < num_files; i++) {
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if (metadata_[i].level == level) {
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sorted_files.push_back(&files_to_import_[i]);
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}
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}
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std::sort(
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sorted_files.begin(), sorted_files.end(),
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[this](const IngestedFileInfo* info1, const IngestedFileInfo* info2) {
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return cfd_->internal_comparator().Compare(
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info1->smallest_internal_key,
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info2->smallest_internal_key) < 0;
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});
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for (size_t i = 0; i + 1 < sorted_files.size(); i++) {
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if (cfd_->internal_comparator().Compare(
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sorted_files[i]->largest_internal_key,
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sorted_files[i + 1]->smallest_internal_key) >= 0) {
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return Status::InvalidArgument("Files have overlapping ranges");
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}
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}
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}
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}
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for (const auto& f : files_to_import_) {
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if (f.num_entries == 0) {
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return Status::InvalidArgument("File contain no entries");
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}
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if (!f.smallest_internal_key.Valid() || !f.largest_internal_key.Valid()) {
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return Status::Corruption("File has corrupted keys");
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}
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}
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// Copy/Move external files into DB
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auto hardlink_files = import_options_.move_files;
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for (auto& f : files_to_import_) {
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const auto path_outside_db = f.external_file_path;
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const auto path_inside_db = TableFileName(
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cfd_->ioptions()->cf_paths, f.fd.GetNumber(), f.fd.GetPathId());
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if (hardlink_files) {
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status =
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fs_->LinkFile(path_outside_db, path_inside_db, IOOptions(), nullptr);
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if (status.IsNotSupported()) {
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// Original file is on a different FS, use copy instead of hard linking
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hardlink_files = false;
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}
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}
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if (!hardlink_files) {
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status = CopyFile(fs_.get(), path_outside_db, path_inside_db, 0,
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db_options_.use_fsync, io_tracer_);
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}
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if (!status.ok()) {
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break;
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}
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f.copy_file = !hardlink_files;
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f.internal_file_path = path_inside_db;
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}
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if (!status.ok()) {
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// We failed, remove all files that we copied into the db
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for (const auto& f : files_to_import_) {
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if (f.internal_file_path.empty()) {
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break;
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}
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const auto s =
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fs_->DeleteFile(f.internal_file_path, IOOptions(), nullptr);
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if (!s.ok()) {
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ROCKS_LOG_WARN(db_options_.info_log,
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"AddFile() clean up for file %s failed : %s",
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f.internal_file_path.c_str(), s.ToString().c_str());
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}
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}
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}
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return status;
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}
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// REQUIRES: we have become the only writer by entering both write_thread_ and
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// nonmem_write_thread_
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Status ImportColumnFamilyJob::Run() {
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Status status;
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edit_.SetColumnFamily(cfd_->GetID());
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// We use the import time as the ancester time. This is the time the data
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// is written to the database.
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int64_t temp_current_time = 0;
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uint64_t oldest_ancester_time = kUnknownOldestAncesterTime;
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uint64_t current_time = kUnknownOldestAncesterTime;
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if (clock_->GetCurrentTime(&temp_current_time).ok()) {
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current_time = oldest_ancester_time =
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static_cast<uint64_t>(temp_current_time);
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}
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for (size_t i = 0; i < files_to_import_.size(); ++i) {
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const auto& f = files_to_import_[i];
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const auto& file_metadata = metadata_[i];
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edit_.AddFile(file_metadata.level, f.fd.GetNumber(), f.fd.GetPathId(),
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f.fd.GetFileSize(), f.smallest_internal_key,
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f.largest_internal_key, file_metadata.smallest_seqno,
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file_metadata.largest_seqno, false, file_metadata.temperature,
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kInvalidBlobFileNumber, oldest_ancester_time, current_time,
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kUnknownFileChecksum, kUnknownFileChecksumFuncName,
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kDisableUserTimestamp, kDisableUserTimestamp);
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// If incoming sequence number is higher, update local sequence number.
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if (file_metadata.largest_seqno > versions_->LastSequence()) {
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versions_->SetLastAllocatedSequence(file_metadata.largest_seqno);
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versions_->SetLastPublishedSequence(file_metadata.largest_seqno);
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versions_->SetLastSequence(file_metadata.largest_seqno);
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}
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}
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return status;
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}
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void ImportColumnFamilyJob::Cleanup(const Status& status) {
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if (!status.ok()) {
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// We failed to add files to the database remove all the files we copied.
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for (const auto& f : files_to_import_) {
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const auto s =
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fs_->DeleteFile(f.internal_file_path, IOOptions(), nullptr);
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if (!s.ok()) {
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ROCKS_LOG_WARN(db_options_.info_log,
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"AddFile() clean up for file %s failed : %s",
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f.internal_file_path.c_str(), s.ToString().c_str());
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}
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}
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} else if (status.ok() && import_options_.move_files) {
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// The files were moved and added successfully, remove original file links
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for (IngestedFileInfo& f : files_to_import_) {
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const auto s =
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fs_->DeleteFile(f.external_file_path, IOOptions(), nullptr);
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if (!s.ok()) {
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ROCKS_LOG_WARN(
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db_options_.info_log,
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"%s was added to DB successfully but failed to remove original "
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"file link : %s",
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f.external_file_path.c_str(), s.ToString().c_str());
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}
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}
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}
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}
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Status ImportColumnFamilyJob::GetIngestedFileInfo(
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const std::string& external_file, uint64_t new_file_number,
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IngestedFileInfo* file_to_import, SuperVersion* sv) {
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file_to_import->external_file_path = external_file;
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// Get external file size
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Status status = fs_->GetFileSize(external_file, IOOptions(),
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&file_to_import->file_size, nullptr);
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if (!status.ok()) {
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return status;
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}
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// Assign FD with number
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file_to_import->fd =
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FileDescriptor(new_file_number, 0, file_to_import->file_size);
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// Create TableReader for external file
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std::unique_ptr<TableReader> table_reader;
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std::unique_ptr<FSRandomAccessFile> sst_file;
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std::unique_ptr<RandomAccessFileReader> sst_file_reader;
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status = fs_->NewRandomAccessFile(external_file, env_options_,
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&sst_file, nullptr);
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if (!status.ok()) {
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return status;
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}
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sst_file_reader.reset(new RandomAccessFileReader(
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std::move(sst_file), external_file, nullptr /*Env*/, io_tracer_));
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status = cfd_->ioptions()->table_factory->NewTableReader(
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TableReaderOptions(
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*cfd_->ioptions(), sv->mutable_cf_options.prefix_extractor.get(),
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env_options_, cfd_->internal_comparator(),
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/*skip_filters*/ false, /*immortal*/ false,
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/*force_direct_prefetch*/ false, /*level*/ -1,
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/*block_cache_tracer*/ nullptr,
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/*max_file_size_for_l0_meta_pin*/ 0, versions_->DbSessionId(),
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/*cur_file_num*/ new_file_number),
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std::move(sst_file_reader), file_to_import->file_size, &table_reader);
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if (!status.ok()) {
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return status;
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}
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// Get the external file properties
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auto props = table_reader->GetTableProperties();
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// Set original_seqno to 0.
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file_to_import->original_seqno = 0;
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// Get number of entries in table
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file_to_import->num_entries = props->num_entries;
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ParsedInternalKey key;
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ReadOptions ro;
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// During reading the external file we can cache blocks that we read into
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// the block cache, if we later change the global seqno of this file, we will
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// have block in cache that will include keys with wrong seqno.
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// We need to disable fill_cache so that we read from the file without
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// updating the block cache.
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ro.fill_cache = false;
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std::unique_ptr<InternalIterator> iter(table_reader->NewIterator(
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ro, sv->mutable_cf_options.prefix_extractor.get(), /*arena=*/nullptr,
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/*skip_filters=*/false, TableReaderCaller::kExternalSSTIngestion));
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// Get first (smallest) key from file
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iter->SeekToFirst();
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Status pik_status =
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ParseInternalKey(iter->key(), &key, db_options_.allow_data_in_errors);
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if (!pik_status.ok()) {
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return Status::Corruption("Corrupted Key in external file. ",
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pik_status.getState());
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}
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file_to_import->smallest_internal_key.SetFrom(key);
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// Get last (largest) key from file
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iter->SeekToLast();
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pik_status =
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ParseInternalKey(iter->key(), &key, db_options_.allow_data_in_errors);
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if (!pik_status.ok()) {
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return Status::Corruption("Corrupted Key in external file. ",
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pik_status.getState());
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}
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file_to_import->largest_internal_key.SetFrom(key);
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file_to_import->cf_id = static_cast<uint32_t>(props->column_family_id);
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file_to_import->table_properties = *props;
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return status;
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}
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} // namespace ROCKSDB_NAMESPACE
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#endif // !ROCKSDB_LITE
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