Deprecate option `periodic_compaction_seconds` for FIFO compaction (#11550)

Summary:
both options `ttl` and `periodic_compaction_seconds` have the same meaning for FIFO compaction, which is redundant and can be confusing to use. For example, setting TTL to 0 does not disable TTL: user needs to also set periodic_compaction_seconds to 0. Another example is that dynamically setting `periodic_compaction_seconds` (surprisingly) has no effect on TTL compaction. This is because FIFO compaction picker internally only looks at value of `ttl`. The value of `ttl` is in `SanitizeOptions()` which take into account the value of `periodic_compaction_seconds`, but dynamically setting an option does not invoke this method.

This PR clarifies the usage of both options for FIFO compaction: only `ttl` should be used, `periodic_compaction_seconds` will not have any effect on FIFO compaction.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11550

Test Plan:
- updated existing unit test `DBOptionsTest.SanitizeFIFOPeriodicCompaction`
- checked existing values of both options in feature matrix: https://fburl.com/daiquery/xxd0gs9w. All current uses cases either have `periodic_compaction_seconds = 0` or have `periodic_compaction_seconds > ttl`, so should not cause change of behavior.

Reviewed By: ajkr

Differential Revision: D46902959

Pulled By: cbi42

fbshipit-source-id: a9ede235b276783b4906aaec443551fa62ceff4c

db/column_family.cc

@@ -382,8 +382,8 @@ ColumnFamilyOptions SanitizeOptions(const ImmutableDBOptions& db_options,
 
   const uint64_t kAdjustedTtl = 30 * 24 * 60 * 60;
   if (result.ttl == kDefaultTtl) {
-    if (is_block_based_table &&
-        result.compaction_style != kCompactionStyleFIFO) {
+    if (is_block_based_table) {
+      // For FIFO, max_open_files is checked in ValidateOptions().
       result.ttl = kAdjustedTtl;
     } else {
       result.ttl = 0;
@@ -403,16 +403,12 @@ ColumnFamilyOptions SanitizeOptions(const ImmutableDBOptions& db_options,
       result.periodic_compaction_seconds = kAdjustedPeriodicCompSecs;
     }
   } else {
-    // result.compaction_style == kCompactionStyleFIFO
-    if (result.ttl == 0) {
-      if (is_block_based_table) {
-        if (result.periodic_compaction_seconds == kDefaultPeriodicCompSecs) {
-          result.periodic_compaction_seconds = kAdjustedPeriodicCompSecs;
-        }
-        result.ttl = result.periodic_compaction_seconds;
-      }
-    } else if (result.periodic_compaction_seconds != 0) {
-      result.ttl = std::min(result.ttl, result.periodic_compaction_seconds);
+    if (result.periodic_compaction_seconds != kDefaultPeriodicCompSecs &&
+        result.periodic_compaction_seconds > 0) {
+      ROCKS_LOG_WARN(
+          db_options.info_log.get(),
+          "periodic_compaction_seconds does not support FIFO compaction. You"
+          "may want to set option TTL instead.");
     }
   }
 

db/db_options_test.cc

@@ -880,9 +880,13 @@ TEST_F(DBOptionsTest, SanitizeFIFOPeriodicCompaction) {
   Options options;
   options.compaction_style = kCompactionStyleFIFO;
   options.env = CurrentOptions().env;
+  // Default value allows RocksDB to set ttl to 30 days.
+  ASSERT_EQ(30 * 24 * 60 * 60, dbfull()->GetOptions().ttl);
+
+  // Disable
   options.ttl = 0;
   Reopen(options);
-  ASSERT_EQ(30 * 24 * 60 * 60, dbfull()->GetOptions().ttl);
+  ASSERT_EQ(0, dbfull()->GetOptions().ttl);
 
   options.ttl = 100;
   Reopen(options);
@@ -892,15 +896,12 @@ TEST_F(DBOptionsTest, SanitizeFIFOPeriodicCompaction) {
   Reopen(options);
   ASSERT_EQ(100 * 24 * 60 * 60, dbfull()->GetOptions().ttl);
 
-  options.ttl = 200;
-  options.periodic_compaction_seconds = 300;
-  Reopen(options);
-  ASSERT_EQ(200, dbfull()->GetOptions().ttl);
-
+  // periodic_compaction_seconds should have no effect
+  // on FIFO compaction.
   options.ttl = 500;
   options.periodic_compaction_seconds = 300;
   Reopen(options);
-  ASSERT_EQ(300, dbfull()->GetOptions().ttl);
+  ASSERT_EQ(500, dbfull()->GetOptions().ttl);
 }
 
 TEST_F(DBOptionsTest, SetFIFOCompactionOptions) {

include/rocksdb/advanced_options.h

@@ -858,24 +858,23 @@ struct AdvancedColumnFamilyOptions {
   // Dynamically changeable through SetOptions() API
   bool report_bg_io_stats = false;
 
-  // Files containing updates older than TTL will go through the compaction
-  // process. This usually happens in a cascading way so that those entries
-  // will be compacted to bottommost level/file.
-  // The feature is used to remove stale entries that have been deleted or
-  // updated from the file system.
-  // Pre-req: This needs max_open_files to be set to -1.
-  // In Level: Non-bottom-level files older than TTL will go through the
-  //           compaction process.
-  // In FIFO: Files older than TTL will be deleted.
+  // This option has different meanings for different compaction styles:
+  //
+  // Leveled: Non-bottom-level files with all keys older than TTL will go
+  //    through the compaction process. This usually happens in a cascading
+  //    way so that those entries will be compacted to bottommost level/file.
+  //    The feature is used to remove stale entries that have been deleted or
+  //    updated from the file system.
+  //
+  // FIFO: Files with all keys older than TTL will be deleted. TTL is only
+  //    supported if option max_open_files is set to -1.
+  //
   // unit: seconds. Ex: 1 day = 1 * 24 * 60 * 60
-  // In FIFO, this option will have the same meaning as
-  // periodic_compaction_seconds. Whichever stricter will be used.
   // 0 means disabling.
   // UINT64_MAX - 1 (0xfffffffffffffffe) is special flag to allow RocksDB to
   // pick default.
   //
-  // Default: 30 days for leveled compaction + block based table. disable
-  //          otherwise.
+  // Default: 30 days if using block based table. 0 (disable) otherwise.
   //
   // Dynamically changeable through SetOptions() API
   uint64_t ttl = 0xfffffffffffffffe;
@@ -891,12 +890,9 @@ struct AdvancedColumnFamilyOptions {
   // age is based on the file's last modified time (given by the underlying
   // Env).
   //
-  // Supported in all compaction styles.
+  // Supported in leveled and universal compaction.
   // In Universal compaction, rocksdb will try to do a full compaction when
   // possible, see more in UniversalCompactionBuilder::PickPeriodicCompaction().
-  // In FIFO compaction, this option has the same meaning as TTL and whichever
-  // stricter will be used.
-  // Pre-req: max_open_file == -1.
   // unit: seconds. Ex: 7 days = 7 * 24 * 60 * 60
   //
   // Values:
@@ -905,9 +901,6 @@ struct AdvancedColumnFamilyOptions {
   //     as needed. For now, RocksDB will change this value to 30 days
   //     (i.e 30 * 24 * 60 * 60) so that every file goes through the compaction
   //     process at least once every 30 days if not compacted sooner.
-  //     In FIFO compaction, since the option has the same meaning as ttl,
-  //     when this value is left default, and ttl is left to 0, 30 days will be
-  //     used. Otherwise, min(ttl, periodic_compaction_seconds) will be used.
   //
   // Default: UINT64_MAX - 1 (allow RocksDB to auto-tune)
   //

unreleased_history/behavior_changes/fifo_ttl_periodic_compaction.md

@@ -0,0 +1 @@
+Option `periodic_compaction_seconds` no longer supports FIFO compaction: setting it has no effect on FIFO compactions. FIFO compaction users should only set option `ttl` instead.