MB-47604: Move VBucket (in-mem) purgeSeqno update to PurgedItemContext

Add a new PurgedItemContext (MagmaImplicitCompactionPurgedItemContext)
so that we can pull out the implicit compaction specific logic to update
the VBucket purge seqno from compactionCore and instead update it via
purgedItem/updateRollbackPurgeSeqno.

Change-Id: Ie3b280ced3583f830e68366c8eb6e3d7b4b03bf6
Reviewed-on: http://review.couchbase.org/c/kv_engine/+/163189
Tested-by: Build Bot <[email protected]>
Reviewed-by: Dave Rigby <[email protected]>

Author: BenHuddleston

engines/ep/src/kvstore/magma-kvstore/magma-kvstore.cc

@@ -299,7 +299,11 @@ bool MagmaKVStore::compactionCallBack(MagmaKVStore::MagmaCompactionCB& cbCtx,
         }
         cbCtx.ctx = makeImplicitCompactionContext(vbid);
         cbCtx.implicitCompaction = true;
-        cbCtx.setCtxPurgedItemCtx();
+        cbCtx.ctx->purgedItemCtx->rollbackPurgeSeqnoCtx =
+                std::make_unique<MagmaImplicitCompactionPurgedItemContext>(
+                        cbCtx.ctx->getRollbackPurgeSeqno(),
+                        cbCtx.magmaDbStats,
+                        cbCtx.ctx->maybeUpdateVBucketPurgeSeqno);
     }
     return compactionCore(
             cbCtx, keySlice, metaSlice, valueSlice, userSanitizedItemStr);
@@ -318,13 +322,6 @@ bool MagmaKVStore::compactionCore(MagmaKVStore::MagmaCompactionCB& cbCtx,
     auto seqno = magmakv::getSeqNum(metaSlice);
     auto exptime = magmakv::getExpiryTime(metaSlice);
 
-    // function to update the purge seqno when we're dropping a document if this
-    // method is being called for implicit compaction
-    auto maybeUpdatePurgeSeqno = [&cbCtx, &seqno]() -> void {
-        if (cbCtx.implicitCompaction) {
-            cbCtx.ctx->maybeUpdateVBucketPurgeSeqno(seqno);
-        }
-    };
     auto vbid = cbCtx.vbid;
     if (cbCtx.ctx->droppedKeyCb) {
         // We need to check both committed and prepared documents - if the
@@ -407,7 +404,6 @@ bool MagmaKVStore::compactionCore(MagmaKVStore::MagmaCompactionCB& cbCtx,
 
             if (drop) {
                 cbCtx.ctx->stats.tombstonesPurged++;
-                maybeUpdatePurgeSeqno();
                 cbCtx.ctx->purgedItemCtx->purgedItem(PurgedItemType::Tombstone,
                                                      seqno);
                 return true;

engines/ep/src/kvstore/magma-kvstore/magma-kvstore_rollback_purge_seqno_ctx.h

@@ -39,4 +39,38 @@ class MagmaRollbackPurgeSeqnoCtx : public RollbackPurgeSeqnoCtx {
 
 protected:
     MagmaDbStats& dbStats;
-};
+};
+
+/**
+ * Magma implicit compaction specific update function for the rollback purge
+ * seqno. See also MagmaRollbackPurgeSeqnoCtx and CompactionContext.
+ *
+ * Explicit compactions updated the in memory purge seqno at the end of a
+ * compaction. This purge seqno is used to turn away DcpConsumers that have
+ * fallen too far behind before we open the file to scan. Implicit compaction
+ * is driven entirely by magma though and does not have a corresponding
+ * completion callback. Instead, implicit compaction moves the in memory
+ * vBucket purge seqno whenever we move the rollbackPurgeSeqno. This class
+ * encapsulates the logic to perform the in memory update whenever we update the
+ * rollbackPurgeSeqno.
+ */
+class MagmaImplicitCompactionPurgedItemContext
+    : public MagmaRollbackPurgeSeqnoCtx {
+public:
+    MagmaImplicitCompactionPurgedItemContext(
+            uint64_t purgeSeqno,
+            MagmaDbStats& dbStats,
+            std::function<void(uint64_t)>& maybeUpdateVBucketPurgeSeqno)
+        : MagmaRollbackPurgeSeqnoCtx(purgeSeqno, dbStats),
+          maybeUpdateVBucketPurgeSeqno(maybeUpdateVBucketPurgeSeqno) {
+    }
+
+    void updateRollbackPurgeSeqno(uint64_t seqno) override {
+        MagmaRollbackPurgeSeqnoCtx::updateRollbackPurgeSeqno(seqno);
+
+        maybeUpdateVBucketPurgeSeqno(seqno);
+    }
+
+protected:
+    std::function<void(uint64_t)>& maybeUpdateVBucketPurgeSeqno;
+};