On 04/03/2018 09:36 PM, xiaoyan li wrote:
On Tue, Apr 3, 2018 at 11:15 PM, Mark Nelson <mark.a.nelson@xxxxxxxxx> wrote:On 04/03/2018 09:56 AM, Mark Nelson wrote:On 04/03/2018 08:27 AM, Sage Weil wrote:On Tue, 3 Apr 2018, Li Wang wrote:Hi, Before we move forward, could someone give a test such that the pglog not written into rocksdb at all, to see how much is the performance improvement as the upper bound, it shoule be less than turning on the bluestore_debug_omit_kv_commit+1 (The PetStore behavior doesn't tell us anything about how BlueStore will behave without the pglog overhead.) sageWe do have some testing of the bluestore's behavior, though it's about 6 months old now: - ~1 hour 4K random overwrites to RBD on 1 NVMe OSD - 128 PGs - stats are sloppy since they only appear every ~10 mins *- default min_pg_log_entries = 1500, trim = default, iops = 26.6K* - Default CF - Size: 65.63MB, KeyIn: 22M, KeyDrop: 17M, Flush: 7.858GB - [M] CF - Size: 118.09MB, KeyIn: 302M, KeyDrop: 269M, Flush: 15.847GB <-- with this workload this is pg log and dup op kv entries - [L] CF - Size: 1.00MB, KeyIn: 181K, KeyDrop: 80K, Flush: 0.320GB <-- deferred writes*- min_pg_log_entries = 10, trim = 10, iops = 24.2K* - Default CF - Size: 23.15MB, KeyIn: 21M, KeyDrop: 16M, Flush: 7.538GB - [M] CF - Size: 60.89MB, KeyIn: 277M, KeyDrop: 250M, Flush: 8.884GB <-- with this workload this is pg log and dup op kv entries - [L] CF - Size: 1.12MB, KeyIn: 188K, KeyDrop: 83K, Flush: 0.331GB <-- deferred writes - min_pg_log_entries = 1, trim = 1, *iops = 23.8K* - Default CF - Size: 68.58MB, KeyIn: 22M, KeyDrop: 17M, Flush: 7.936GB - [M] CF - Size: 96.39MB, KeyIn: 302M, KeyDrop: 262M, Flush: 9.289GB <-- with this workload this is pg log and dup op kv entries - [L] CF - Size: 1.04MB, KeyIn: 209K, KeyDrop: 92K, Flush: 0.368GB <-- deferred writes - min_pg_log_entires = 3000, trim = 1, *iops = 25.8K* * The actual performance variation here I think is much less important than the KeyIn behavior. The NVMe devices in these tests are fast enough to absorb a fair amount of overhead.Ugh, sorry. That will teach me to talk in meeting and paste at the same time. Those were the wrong stats. Here are the right ones:- ~1 hour 4K random overwrites to RBD on 1 NVMe OSD - 128 PGs - stats are sloppy since they only appear every ~10 mins - min_pg_log_entries = 3000, trim = default, pginfo hack, iops = 27.8K - Default CF - Size: 23.15MB, KeyIn: 24M, KeyDrop: 19M, Flush: 8.662GB - [M] CF - Size: 159.97MB, KeyIn: 162M, KeyDrop: 139M, Flush: 10.335GB <-- with this workload this is pg log and dup op kv entries - [L] CF - Size: 1.39MB, KeyIn: 201K, KeyDrop: 89K, Flush: 0.355GB <-- deferred writes - min_pg_log_entries = 3000, trim = default iops = 28.3K - Default CF - Size: 23.13MB, KeyIn: 25M, KeyDrop: 19M, Flush: 8.762GB - [M] CF - Size: 159.97MB, KeyIn: 202M, KeyDrop: 175M, Flush: 16.890GB <-- with this workload this is pg log and dup op kv entries - [L] CF - Size: 0.86MB, KeyIn: 201K, KeyDrop: 89K, Flush: 0.355GB <-- deferred writes - default min_pg_log_entries = 1500, trim = default, iops = 26.6K - Default CF - Size: 65.63MB, KeyIn: 22M, KeyDrop: 17M, Flush: 7.858GB - [M] CF - Size: 118.09MB, KeyIn: 302M, KeyDrop: 269M, Flush: 15.847GB <-- with this workload this is pg log and dup op kv entries - [L] CF - Size: 1.00MB, KeyIn: 181K, KeyDrop: 80K, Flush: 0.320GB <-- deferred writes - min_pg_log_entries = 10, trim = 10, iops = 24.2K - Default CF - Size: 23.15MB, KeyIn: 21M, KeyDrop: 16M, Flush: 7.538GB - [M] CF - Size: 60.89MB, KeyIn: 277M, KeyDrop: 250M, Flush: 8.884GB <-- with this workload this is pg log and dup op kv entries - [L] CF - Size: 1.12MB, KeyIn: 188K, KeyDrop: 83K, Flush: 0.331GB <-- deferred writes - min_pg_log_entries = 1, trim = 1, iops = 23.8K - Default CF - Size: 68.58MB, KeyIn: 22M, KeyDrop: 17M, Flush: 7.936GB - [M] CF - Size: 96.39MB, KeyIn: 302M, KeyDrop: 262M, Flush: 9.289GB <-- with this workload this is pg log and dup op kv entries - [L] CF - Size: 1.04MB, KeyIn: 209K, KeyDrop: 92K, Flush: 0.368GB <-- deferred writes - min_pg_log_entires = 3000, trim = 1, iops = 25.8KHi Mark, do you extract above results from compaction stats in Rocksdb LOG?
Correct, except for the IOPS numbers which were from the client benchmark.
** Compaction Stats [default] ** Level Files Size Score Read(GB) Rn(GB) Rnp1(GB) Write(GB) Wnew(GB) Moved(GB) W-Amp Rd(MB/s) Wr(MB/s) Comp(sec) Comp(cnt) Avg(sec) KeyIn KeyDrop ---------------------------------------------------------------------------------------------------------------------------------------------------------- L0 6/0 270.47 MB 1.1 0.0 0.0 0.0 0.2 0.2 0.0 1.0 0.0 154.3 1 4 0.329 0 0 L1 3/0 190.94 MB 0.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 0 0.000 0 0 Sum 9/0 461.40 MB 0.0 0.0 0.0 0.0 0.2 0.2 0.0 1.0 0.0 154.3 1 4 0.329 0 0 Int 0/0 0.00 KB 0.0 0.0 0.0 0.0 0.2 0.2 0.0 1.0 0.0 154.3 1 4 0.329 0 0 Uptime(secs): 9.9 total, 9.9 interval Flush(GB): cumulative 0.198, interval 0.198Note specifically how the KeyIn rate drops with the min_pg_log_entries increased (ie disable dup_ops) and hacking out pginfo. I suspect that commenting out log_operation would reduce the KeyIn rate significantly further. Again these drives can absorb a lot of this so the improvement in iops is fairly modest (and setting min_pg_log_entries low actually hurts!), but this isn't just about performance, it's about the behavior that we invoke. The Petstore results absolutely show us that on very fast storage we see a dramatic CPU usage reduction by removing log_operation and pginfo, so I think we should focus on what kind of behavior we want pglog/pginfo/dup_ops to invoke. Mark*Cheers, Li Wang 2018-04-02 13:29 GMT+08:00 xiaoyan li <wisher2003@xxxxxxxxx>:Hi all, Based on your above discussion about pglog, I have the following rough design. Please help to give your suggestions. There will be three partitions: raw part for customer IOs, Bluefs for Rocksdb, and pglog partition. The former two partitions are same as current. The pglog partition is splitted into 1M blocks. We allocate blocks for ring buffers per pg. We will have such following data: Allocation bitmap (just in memory) The pglog partition has a bitmap to record which block is allocated or not. We can rebuild it through pg->allocated_block_list when starting, and no need to store it in persistent disk. But we will store basic information about the pglog partition in Rocksdb, like block size, block number etc when the objectstore is initialized. Pg -> allocated_blocks_list When a pg is created and IOs start, we can allocate a block for every pg. Every pglog entry is less than 300 bytes, 1M can store 3495 entries. When total pglog entries increase and exceed the number, we can add a new block to the pg. Pg->start_position Record the oldest valid entry per pg. Pg->next_position Record the next entry to add per pg. The data will be updated frequently, but Rocksdb is suitable for its io mode, and most of data will be merged. Updated Bluestore write progess: When writing data to disk (before metadata updating), we can append the pglog entry to its ring buffer in parallel. After that, submit pg ring buffer changes like pg->next_position, and current other metadata changes to Rocksdb. On Fri, Mar 30, 2018 at 6:23 PM, Varada Kari <varada.kari@xxxxxxxxx> wrote:On Fri, Mar 30, 2018 at 1:01 PM, Li Wang <laurence.liwang@xxxxxxxxx> wrote:Hi, If we wanna store pg log in a standalone ring buffer, another candidate is the deferred write, why not use the ring buffer as the journal for 4K random write, it should be much more lightweight than rocksdbIt will be similar to FileStore implementation, for small writes. That comes with the same alignment issues and given write amplification. Rocksdb nicely abstracts that and we don't make it to L0 files because of WAL handling. VaradaCheers, Li Wang 2018-03-30 4:04 GMT+08:00 Sage Weil <sweil@xxxxxxxxxx>:On Wed, 28 Mar 2018, Matt Benjamin wrote:On Wed, Mar 28, 2018 at 1:44 PM, Mark Nelson <mnelson@xxxxxxxxxx> wrote:On 03/28/2018 12:21 PM, Adam C. Emerson wrote: 2) It sure feels like conceptually the pglog should be represented as a per-pg ring buffer rather than key/value data. Maybe there are really important reasons that it shouldn't be, but I don't currently see them. As far as the objectstore is concerned, it seems to me like there are valid reasons to provide some kind of log interface and perhaps that should be used for pg_log. That sort of opens the door for different object store implementations fulfilling that functionality in whatever ways the author deems fit.In the reddit lingo, pretty much this. We should be concentrating on this direction, or ruling it out.Yeah, +1 It seems like step 1 is a proof of concept branch that encodes pg_log_entry_t's and writes them to a simple ring buffer. The first questions to answer is (a) whether this does in fact improve things significantly and (b) whether we want to have an independent ring buffer for each PG or try to mix them into one big one for the whole OSD (or maybe per shard). The second question is how that fares on HDDs. My guess is that the current rocksdb strategy is better because it reduces the number of IOs and the additional data getting compacted (and CPU usage) isn't the limiting factor on HDD perforamnce (IOPS are). (But maybe we'll get lucky and the new strategy will be best for both HDD and SSD..) Then we have to modify PGLog to be a complete implementation. A strict ring buffer probably won't work because the PG log might not trim and because log entries are variable length, so there'll probably need to be some simple mapping table (vs a trivial start/end ring buffer position) to deal with that. We have to trim the log periodically, so every so many entries we may want to realign with a min_alloc_size boundary. We someones have to back up and rewrite divergent portions of the log (during peering) so we'll need to sort out whether that is a complete reencode/rewrite or whether we keep encoded entries in ram (individually or in chunks), etc etc. sage -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html-- Best wishes Lisa-- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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