Remove incremental ID from background thread pool names (#9165)

Summary:
`pthread_setname_np()` fails on attempts to assign oversized names like
"rocksdb:bottom10", which resulted in some thread name updates being
lost. We do not need the ID suffix so I removed it.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9165

Test Plan:
```
$ TEST_TMPDIR=/dev/shm ./db_bench -benchmarks=fillrandom -max_background_flushes=123 -max_background_compactions=456 -num_bottom_pri_threads=789 -duration=60
```

While above is running:
```
$ ps -o 'comm' -Lp `pidof db_bench` | grep '^rocksdb:' | sort | uniq -c
    789 rocksdb:bottom
    123 rocksdb:high
    456 rocksdb:low
```

Reviewed By: pdillinger

Differential Revision: D32415077

Pulled By: ajkr

fbshipit-source-id: a0e013101e26a78bc5eca73509293ef4bf22254f

HISTORY.md

@@ -23,16 +23,15 @@
 * `TransactionUtil::CheckKeyForConflicts` can also perform conflict-checking based on user-defined timestamps in addition to sequence numbers.
 * Removed `GenericRateLimiter`'s minimum refill bytes per period previously enforced.
 
-### Public Interface Change
-* When options.ttl is used with leveled compaction with compactinon priority kMinOverlappingRatio, files exceeding half of TTL value will be prioritized more, so that by the time TTL is reached, fewer extra compactions will be scheduled to clear them up. At the same time, when compacting files with data older than half of TTL, output files may be cut off based on those files' boundaries, in order for the early TTL compaction to work properly.
-* Info log ("LOG" file) lines now print a system-wide thread ID from `gettid()` when the compiler flags/glibc version make it available instead of the process-local `pthread_self()`. For all users, the thread ID format is changed from hexadecimal to decimal integer.
-
 ### Public API change
+* When options.ttl is used with leveled compaction with compactinon priority kMinOverlappingRatio, files exceeding half of TTL value will be prioritized more, so that by the time TTL is reached, fewer extra compactions will be scheduled to clear them up. At the same time, when compacting files with data older than half of TTL, output files may be cut off based on those files' boundaries, in order for the early TTL compaction to work properly.
 * Made FileSystem extend the Customizable class and added a CreateFromString method.  Implementations need to be registered with the ObjectRegistry and to implement a Name() method in order to be created via this method.
 * Clarified in API comments that RocksDB is not exception safe for callbacks and custom extensions. An exception propagating into RocksDB can lead to undefined behavior, including data loss, unreported corruption, deadlocks, and more.
 * Marked `WriteBufferManager` as `final` because it is not intended for extension.
 * Add API `FSDirectory::FsyncWithDirOptions()`, which provides extra information like directory fsync reason in `DirFsyncOptions`. File system like btrfs is using that to skip directory fsync for creating a new file, or when renaming a file, fsync the target file instead of the directory, which improves the `DB::Open()` speed by ~20%.
 * `DB::Open()` is not going be blocked by obsolete file purge if `DBOptions::avoid_unnecessary_blocking_io` is set to true.
+* In builds where glibc provides `gettid()`, info log ("LOG" file) lines now print a system-wide thread ID from `gettid()` instead of the process-local `pthread_self()`. For all users, the thread ID format is changed from hexadecimal to decimal integer.
+* In builds where glibc provides `pthread_setname_np()`, the background thread names no longer contain an ID suffix. For example, "rocksdb:bottom7" (and all other threads in the `Env::Priority::BOTTOM` pool) are now named "rocksdb:bottom". Previously large thread pools could breach the name size limit (e.g., naming "rocksdb:bottom10" would fail).
 
 ### Performance Improvements
 * Released some memory related to filter construction earlier in `BlockBasedTableBuilder` for `FullFilter` and `PartitionedFilter` case (#9070)

util/threadpool_imp.cc

@@ -347,7 +347,6 @@ void ThreadPoolImpl::Impl::StartBGThreads() {
     for (char c : thread_priority) {
       thread_name_stream << static_cast<char>(tolower(c));
     }
-    thread_name_stream << bgthreads_.size();
     pthread_setname_np(th_handle, thread_name_stream.str().c_str());
 #endif
 #endif