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rocksdb/utilities/redis/redis_lists.cc

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// Copyright 2013 Facebook
/**
* A (persistent) Redis API built using the rocksdb backend.
* Implements Redis Lists as described on: http://redis.io/commands#list
*
* @throws All functions may throw a RedisListException on error/corruption.
*
* @notes Internally, the set of lists is stored in a rocksdb database,
* mapping keys to values. Each "value" is the list itself, storing
* some kind of internal representation of the data. All the
* representation details are handled by the RedisListIterator class.
* The present file should be oblivious to the representation details,
* handling only the client (Redis) API, and the calls to rocksdb.
*
* @TODO Presently, all operations take at least O(NV) time where
* N is the number of elements in the list, and V is the average
* number of bytes per value in the list. So maybe, with merge operator
* we can improve this to an optimal O(V) amortized time, since we
* wouldn't have to read and re-write the entire list.
*
* @author Deon Nicholas (dnicholas@fb.com)
*/
#ifndef ROCKSDB_LITE
#include "redis_lists.h"
#include <iostream>
#include <memory>
#include <cmath>
#include "rocksdb/slice.h"
#include "util/coding.h"
namespace rocksdb
{
/// Constructors
RedisLists::RedisLists(const std::string& db_path,
Options options, bool destructive)
: put_option_(),
get_option_() {
// Store the name of the database
db_name_ = db_path;
// If destructive, destroy the DB before re-opening it.
if (destructive) {
DestroyDB(db_name_, Options());
}
// Now open and deal with the db
DB* db;
Status s = DB::Open(options, db_name_, &db);
if (!s.ok()) {
std::cerr << "ERROR " << s.ToString() << std::endl;
assert(false);
}
db_ = std::unique_ptr<DB>(db);
}
/// Accessors
// Number of elements in the list associated with key
// : throws RedisListException
int RedisLists::Length(const std::string& key) {
// Extract the string data representing the list.
std::string data;
db_->Get(get_option_, key, &data);
// Return the length
RedisListIterator it(data);
return it.Length();
}
// Get the element at the specified index in the (list: key)
// Returns <empty> ("") on out-of-bounds
// : throws RedisListException
bool RedisLists::Index(const std::string& key, int32_t index,
std::string* result) {
// Extract the string data representing the list.
std::string data;
db_->Get(get_option_, key, &data);
// Handle REDIS negative indices (from the end); fast iff Length() takes O(1)
if (index < 0) {
index = Length(key) - (-index); //replace (-i) with (N-i).
}
// Iterate through the list until the desired index is found.
int curIndex = 0;
RedisListIterator it(data);
while(curIndex < index && !it.Done()) {
++curIndex;
it.Skip();
}
// If we actually found the index
if (curIndex == index && !it.Done()) {
Slice elem;
it.GetCurrent(&elem);
if (result != nullptr) {
*result = elem.ToString();
}
return true;
} else {
return false;
}
}
// Return a truncated version of the list.
// First, negative values for first/last are interpreted as "end of list".
// So, if first == -1, then it is re-set to index: (Length(key) - 1)
// Then, return exactly those indices i such that first <= i <= last.
// : throws RedisListException
std::vector<std::string> RedisLists::Range(const std::string& key,
int32_t first, int32_t last) {
// Extract the string data representing the list.
std::string data;
db_->Get(get_option_, key, &data);
// Handle negative bounds (-1 means last element, etc.)
int listLen = Length(key);
if (first < 0) {
first = listLen - (-first); // Replace (-x) with (N-x)
}
if (last < 0) {
last = listLen - (-last);
}
// Verify bounds (and truncate the range so that it is valid)
first = std::max(first, 0);
last = std::min(last, listLen-1);
int len = std::max(last-first+1, 0);
// Initialize the resulting list
std::vector<std::string> result(len);
// Traverse the list and update the vector
int curIdx = 0;
Slice elem;
for (RedisListIterator it(data); !it.Done() && curIdx<=last; it.Skip()) {
if (first <= curIdx && curIdx <= last) {
it.GetCurrent(&elem);
result[curIdx-first].assign(elem.data(),elem.size());
}
++curIdx;
}
// Return the result. Might be empty
return result;
}
// Print the (list: key) out to stdout. For debugging mostly. Public for now.
void RedisLists::Print(const std::string& key) {
// Extract the string data representing the list.
std::string data;
db_->Get(get_option_, key, &data);
// Iterate through the list and print the items
Slice elem;
for (RedisListIterator it(data); !it.Done(); it.Skip()) {
it.GetCurrent(&elem);
std::cout << "ITEM " << elem.ToString() << std::endl;
}
//Now print the byte data
RedisListIterator it(data);
std::cout << "==Printing data==" << std::endl;
std::cout << data.size() << std::endl;
std::cout << it.Size() << " " << it.Length() << std::endl;
Slice result = it.WriteResult();
std::cout << result.data() << std::endl;
if (true) {
std::cout << "size: " << result.size() << std::endl;
const char* val = result.data();
for(int i=0; i<(int)result.size(); ++i) {
std::cout << (int)val[i] << " " << (val[i]>=32?val[i]:' ') << std::endl;
}
std::cout << std::endl;
}
}
/// Insert/Update Functions
/// Note: The "real" insert function is private. See below.
// InsertBefore and InsertAfter are simply wrappers around the Insert function.
int RedisLists::InsertBefore(const std::string& key, const std::string& pivot,
const std::string& value) {
return Insert(key, pivot, value, false);
}
int RedisLists::InsertAfter(const std::string& key, const std::string& pivot,
const std::string& value) {
return Insert(key, pivot, value, true);
}
// Prepend value onto beginning of (list: key)
// : throws RedisListException
int RedisLists::PushLeft(const std::string& key, const std::string& value) {
// Get the original list data
std::string data;
db_->Get(get_option_, key, &data);
// Construct the result
RedisListIterator it(data);
it.Reserve(it.Size() + it.SizeOf(value));
it.InsertElement(value);
// Push the data back to the db and return the length
db_->Put(put_option_, key, it.WriteResult());
return it.Length();
}
// Append value onto end of (list: key)
// TODO: Make this O(1) time. Might require MergeOperator.
// : throws RedisListException
int RedisLists::PushRight(const std::string& key, const std::string& value) {
// Get the original list data
std::string data;
db_->Get(get_option_, key, &data);
// Create an iterator to the data and seek to the end.
RedisListIterator it(data);
it.Reserve(it.Size() + it.SizeOf(value));
while (!it.Done()) {
it.Push(); // Write each element as we go
}
// Insert the new element at the current position (the end)
it.InsertElement(value);
// Push it back to the db, and return length
db_->Put(put_option_, key, it.WriteResult());
return it.Length();
}
// Set (list: key)[idx] = val. Return true on success, false on fail.
// : throws RedisListException
bool RedisLists::Set(const std::string& key, int32_t index,
const std::string& value) {
// Get the original list data
std::string data;
db_->Get(get_option_, key, &data);
// Handle negative index for REDIS (meaning -index from end of list)
if (index < 0) {
index = Length(key) - (-index);
}
// Iterate through the list until we find the element we want
int curIndex = 0;
RedisListIterator it(data);
it.Reserve(it.Size() + it.SizeOf(value)); // Over-estimate is fine
while(curIndex < index && !it.Done()) {
it.Push();
++curIndex;
}
// If not found, return false (this occurs when index was invalid)
if (it.Done() || curIndex != index) {
return false;
}
// Write the new element value, and drop the previous element value
it.InsertElement(value);
it.Skip();
// Write the data to the database
// Check status, since it needs to return true/false guarantee
Status s = db_->Put(put_option_, key, it.WriteResult());
// Success
return s.ok();
}
/// Delete / Remove / Pop functions
// Trim (list: key) so that it will only contain the indices from start..stop
// Invalid indices will not generate an error, just empty,
// or the portion of the list that fits in this interval
// : throws RedisListException
bool RedisLists::Trim(const std::string& key, int32_t start, int32_t stop) {
// Get the original list data
std::string data;
db_->Get(get_option_, key, &data);
// Handle negative indices in REDIS
int listLen = Length(key);
if (start < 0) {
start = listLen - (-start);
}
if (stop < 0) {
stop = listLen - (-stop);
}
// Truncate bounds to only fit in the list
start = std::max(start, 0);
stop = std::min(stop, listLen-1);
// Construct an iterator for the list. Drop all undesired elements.
int curIndex = 0;
RedisListIterator it(data);
it.Reserve(it.Size()); // Over-estimate
while(!it.Done()) {
// If not within the range, just skip the item (drop it).
// Otherwise, continue as usual.
if (start <= curIndex && curIndex <= stop) {
it.Push();
} else {
it.Skip();
}
// Increment the current index
++curIndex;
}
// Write the (possibly empty) result to the database
Status s = db_->Put(put_option_, key, it.WriteResult());
// Return true as long as the write succeeded
return s.ok();
}
// Return and remove the first element in the list (or "" if empty)
// : throws RedisListException
bool RedisLists::PopLeft(const std::string& key, std::string* result) {
// Get the original list data
std::string data;
db_->Get(get_option_, key, &data);
// Point to first element in the list (if it exists), and get its value/size
RedisListIterator it(data);
if (it.Length() > 0) { // Proceed only if list is non-empty
Slice elem;
it.GetCurrent(&elem); // Store the value of the first element
it.Reserve(it.Size() - it.SizeOf(elem));
it.Skip(); // DROP the first item and move to next
// Update the db
db_->Put(put_option_, key, it.WriteResult());
// Return the value
if (result != nullptr) {
*result = elem.ToString();
}
return true;
} else {
return false;
}
}
// Remove and return the last element in the list (or "" if empty)
// TODO: Make this O(1). Might require MergeOperator.
// : throws RedisListException
bool RedisLists::PopRight(const std::string& key, std::string* result) {
// Extract the original list data
std::string data;
db_->Get(get_option_, key, &data);
// Construct an iterator to the data and move to last element
RedisListIterator it(data);
it.Reserve(it.Size());
int len = it.Length();
int curIndex = 0;
while(curIndex < (len-1) && !it.Done()) {
it.Push();
++curIndex;
}
// Extract and drop/skip the last element
if (curIndex == len-1) {
assert(!it.Done()); // Sanity check. Should not have ended here.
// Extract and pop the element
Slice elem;
it.GetCurrent(&elem); // Save value of element.
it.Skip(); // Skip the element
// Write the result to the database
db_->Put(put_option_, key, it.WriteResult());
// Return the value
if (result != nullptr) {
*result = elem.ToString();
}
return true;
} else {
// Must have been an empty list
assert(it.Done() && len==0 && curIndex == 0);
return false;
}
}
// Remove the (first or last) "num" occurrences of value in (list: key)
// : throws RedisListException
int RedisLists::Remove(const std::string& key, int32_t num,
const std::string& value) {
// Negative num ==> RemoveLast; Positive num ==> Remove First
if (num < 0) {
return RemoveLast(key, -num, value);
} else if (num > 0) {
return RemoveFirst(key, num, value);
} else {
return RemoveFirst(key, Length(key), value);
}
}
// Remove the first "num" occurrences of value in (list: key).
// : throws RedisListException
int RedisLists::RemoveFirst(const std::string& key, int32_t num,
const std::string& value) {
// Ensure that the number is positive
assert(num >= 0);
// Extract the original list data
std::string data;
db_->Get(get_option_, key, &data);
// Traverse the list, appending all but the desired occurrences of value
int numSkipped = 0; // Keep track of the number of times value is seen
Slice elem;
RedisListIterator it(data);
it.Reserve(it.Size());
while (!it.Done()) {
it.GetCurrent(&elem);
if (elem == value && numSkipped < num) {
// Drop this item if desired
it.Skip();
++numSkipped;
} else {
// Otherwise keep the item and proceed as normal
it.Push();
}
}
// Put the result back to the database
db_->Put(put_option_, key, it.WriteResult());
// Return the number of elements removed
return numSkipped;
}
// Remove the last "num" occurrences of value in (list: key).
// TODO: I traverse the list 2x. Make faster. Might require MergeOperator.
// : throws RedisListException
int RedisLists::RemoveLast(const std::string& key, int32_t num,
const std::string& value) {
// Ensure that the number is positive
assert(num >= 0);
// Extract the original list data
std::string data;
db_->Get(get_option_, key, &data);
// Temporary variable to hold the "current element" in the blocks below
Slice elem;
// Count the total number of occurrences of value
int totalOccs = 0;
for (RedisListIterator it(data); !it.Done(); it.Skip()) {
it.GetCurrent(&elem);
if (elem == value) {
++totalOccs;
}
}
// Construct an iterator to the data. Reserve enough space for the result.
RedisListIterator it(data);
int bytesRemoved = std::min(num,totalOccs)*it.SizeOf(value);
it.Reserve(it.Size() - bytesRemoved);
// Traverse the list, appending all but the desired occurrences of value.
// Note: "Drop the last k occurrences" is equivalent to
// "keep only the first n-k occurrences", where n is total occurrences.
int numKept = 0; // Keep track of the number of times value is kept
while(!it.Done()) {
it.GetCurrent(&elem);
// If we are within the deletion range and equal to value, drop it.
// Otherwise, append/keep/push it.
if (elem == value) {
if (numKept < totalOccs - num) {
it.Push();
++numKept;
} else {
it.Skip();
}
} else {
// Always append the others
it.Push();
}
}
// Put the result back to the database
db_->Put(put_option_, key, it.WriteResult());
// Return the number of elements removed
return totalOccs - numKept;
}
/// Private functions
// Insert element value into (list: key), right before/after
// the first occurrence of pivot
// : throws RedisListException
int RedisLists::Insert(const std::string& key, const std::string& pivot,
const std::string& value, bool insert_after) {
// Get the original list data
std::string data;
db_->Get(get_option_, key, &data);
// Construct an iterator to the data and reserve enough space for result.
RedisListIterator it(data);
it.Reserve(it.Size() + it.SizeOf(value));
// Iterate through the list until we find the element we want
Slice elem;
bool found = false;
while(!it.Done() && !found) {
it.GetCurrent(&elem);
// When we find the element, insert the element and mark found
if (elem == pivot) { // Found it!
found = true;
if (insert_after == true) { // Skip one more, if inserting after it
it.Push();
}
it.InsertElement(value);
} else {
it.Push();
}
}
// Put the data (string) into the database
if (found) {
db_->Put(put_option_, key, it.WriteResult());
}
// Returns the new (possibly unchanged) length of the list
return it.Length();
}
} // namespace rocksdb
#endif // ROCKSDB_LITE